I have IE 6 on Linux working fairly well with OWA, on an Exchange 2007 setup, in "Premium" mode now. There is a small bit of flicker, as it does its refreshing. The powers-that-be decided we should bow to the few and change our email system to eXchange. I was so happy to be thrown back into the '90s that I took different position in the company (not the same one I did the Linux email server at). To spare you the rant, let's just say been there, done that, still own stock in Maalox. Though Microsoft treats even IE users like they are dregs, for not using Outlook, OWA is the only option I have for interfacing with calendar (for now) and a VMWare instance just isn't worth it for only doing that.

Note: The following is for informational and educational purposes only. The following may or may not involve violating software licensing. It is up to you to determine if your situation meets any such legalieze in a software's licensing text.

I started with installing Wine, cabextract, and ies4linux. The current versions I have (FC6) are:
wine-0.9.46
cabextract-1.1
ies4linux-2.99.0 (beta)

Note: On Fedora 8 with Wine version 0.9.55 I had to use ies4linux-2.99.0.1 to get it to complete the install. With the F8 computer I had installed from the KDE version of the Live CD and needed to add wget. If the download part of the install fails, make sure you have wget installed.

One older version of Wine caused the URL bar in IE not to function. I cannot recall the specific one. The last two updates versions have been fine though. If you use the older "stable" version of ies4linux, you will get a cert validation error, but the encryption will still work, and you'll have to fix a handful of other things.

Some steps may not be needed for OWA, but I needed them for another ActiveX-based interface I'm trying to get working.

First thing, of course, is to get IE installed and working under Wine. Ies4Linux is the easiest way to do this. Just follow their steps for getting it installed.
http://www.tatanka.com.br/ies4linux/
http://www.tatanka.com.br/ies4linux/news/49

Additional steps I took once ies4linux was installed:
[01/31/2008 - updated w/ recommendations]
[02/23/2008 - updated for additional clarification]

1. Install Java:
   • Run IE6
   • Go to http://java.com (ala typing in the "Address" box)
   • Do the install (should be for Win98) using on-line version (give it a second to launch, it can be slow). Be sure to pick the "Open" button in the dialog, not the "Save" one.
2. Fix java blanking the screen (DirectX thing) if you have issues when running the Java Console (see the "Tools" menu in IE). I don't seem to have this issue now with a clean install of Fedora 8, with all updates, and wine-0.9.55-2.fc8.:
   • Close IE if it is open.
   • Open a console/terminal window as your regular user ID. Then execute (note the "$" is the command prompt, do not type it. Replace your login ID where "[user]" is shown below.):
     • $ export WINEPREFIX="/home/[user]/.ies4linux/ie6"
     • $ wine regedit
   • In the registry editor window navigate to:
     HKEY_CURRENT_USER\Software\JavaSoft\Java2D\1.5.0_14
   • Set "DXAcceleration" to "0" (zero).
   • Close regedit.
   • Run IE and test to confirm Java Console runs without screen blanking issues.
3. Make IE report Win2k when Wine is Win98 so OWA 2k7 works in Premium mode:
   • Close IE if it is open.
   • Open a console/terminal window as your regular user ID. Then execute (note the "$" is the command prompt., do not type it. Replace your login ID where "[user]" is shown below.)
     • $ export WINEPREFIX="/home/[user]/.ies4linux/ie6"
     • $ wine regedit
   • In the registry editor window navigate to:
     HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Internet Settings\User Agent\
   • Select the "Edit" menu -> New -> Key. For the key name enter:
     Post Platform
   • With "Post Platform" selected: Edit menu -> New -> String Value. For the name enter:
     Windows NT 5.1
   • Click "OK", then double-click the new item named "Windows NT 5.1" and set the value:
     This String Doesn’t Matter I think
   • Select "User Agent" key again
   • Select the "Edit" menu -> New -> Key. For the key name enter:
     Pre Platform
   • With "Pre Platform" selected: Edit menu -> New -> String Value. For the name enter:
     Windows NT 5.1
   • Click "OK", then double-click the new item named "Windows NT 5.1" and set the value:
     This String Doesn’t Matter I think
   • Close regedit
   • Run IE and test logging into OWA. On the login page it should now allow you to select either premium mode or lite mode.

Few more tidbits I've dug up. The only way to view a shared calendar via OWA is with IE and you must manually compose the URL like:
https://[owa_host]/owa/[full_email_address]/?cmd=contents&f=calendar
This will not work with non-IE browsers, ala Firefox. Also, once you access the shared calendar URL and login you can change the [full_email_address] part of the URL in the same browser session and not have to log in again.

You can add "&view=weekly" on the end of the URL to have it default to the week view. See here for more:
http://msexchangeteam.com/archive/2006/11/28/431665.aspx8

Interesting "bug" in OWA 2k7: If the user who's calendar you're trying to view has never signed into OWA you'll be presented with the select language page and won't be able to access their calendar. Great way to find if someone primarily uses Outlook.

Right now I'm using IE to only display my calendar and Thunderbird, via IMAP, for email. Even MS says there are issues if you don't use the emailed invitation to accept/decline. I did use only OWA for about a month, until they finally turned on IMAP. Yes, IMAP with Exchange, compared to an email server made to do IMAP, is flaky. But being able to use a program that makes sense to you and keeps you efficient is better than having one way only shoved down your throat.

To get your account disk usage in OWA you must use IE in Premium mode. Once logged in, hover over your account name at the top of the folder tree on the left. It will pop-up as a tool-tip.

Links to other's work I used to figure this all out (hey, why figure it out if someone else already has):
http://www.gagme.com/greg/linux/activex-linux.php
http://wine-review.blogspot.com/2007/08/ies-4-linux-internet-explorer-50-55-60.html
http://rmathew.blogspot.com/2007/04/running-java-applets-in-internet.html