Here is something you could check for using exchange with Thunderbird http://www.google.nl/search?q=thunderbi ... =firefox-a
You could also try this site for setting up Thunderbird http://mozilla.gunnars.net/thunderbird_mail_setup.html
And heres a freaking big site with all you can and want to do with Thunderbird. http://email.about.com/od/mozillathunde ... ecrets.htm
But next to this all, im still thinking that dropping Outlook is the best thing to do in your roomies case. If he can get Gmail on his IPhone, then why still use Outlook? And im sure his Iphone can handle IMAP, POP3 and Exchange, so let him set up those accounts on his IPhone and he is done. No more desktop apps for gmail or exchange. Everything from his phone, like im doing. Just one spot that check everything accept pop3 cause you have to fetch pop3 manually.
edit: Be sure you you close the www connection to the pc where Outlook is installed, because IMAP works both ways. If you delete messages in Outlook, they are also deleted in Gmail and on the Iphone. I learned that the hard way. So kill the internet connection, pull the cable out, or pull the plug from your isp modem and then backup your outlook messages and contacts is needed, and then deinstall Outlook if wanted. You could also just stop using Outlook ofc. In my case, when I got my laptop, i didnt install any Office program. None. I didnt want to spend any money on stuff that doesnt work like it should. So im using gmail and OpenOffice, together with my android Samsung Galaxy S and the mobile app from Dropbox im done and can rule the world.
@MrGroove: Maybe worth a article? The dropbox app for Android or Iphone? Some review thingy or maybe just fun stuff you can do with dropbox?