For Office apps theres OpenOffice.org , its very nice IMO and it pretty compatible with MS Office(like 90-95%), and it can save in MS Office formates. I've only noticed a small difference/compatibility problem with graphs in the spread sheet and it is something very minor and might have actually been able to fix it, I just did not have the time to do so.
Battlefield 2142 work eventually but I doubt it would right now since its a fairly new game. Give it time and it might, but still might not... We just need developers who do the game make them use Open Source/OpenGL and then Linux would run games pretty well.
For AIM or any windows messenger client theres GAIM and Kopete. Both let you use all the major IM clients (AIM, MSN, Yahoo, Jabber, etc.) And you can have all your friends from MSN and AIM on just that one IM client. Pretty sweet IMO.
Outlook Express theres Evolution, Kmail, Kontact, Thunderbird. All are pretty nice, and have a ton of features(Notes, Personal Contacts, Calender, to-do list, etc.)
F@H is out for Linux too and it'll work on the *BSD Unix too.
How to get all that? All but the Folding at home is pretty much standard in all the main Linux Distros. KDE and GNOME both have all their own apps for each task. Its really got quite a few features that I know some people don't think about or think that Linux might be lacking. (I'm in no way directing this to you are anyone else.) As long as you still to one of the main Linux distros (SuSE, Fedora, *buntu, Debian, Slackware, Gentoo) you'll find these apps pretty mush by default. When without OpenOffice, both KDE and GNOME have their own office suit but there pretty minimal. OOo is much better IMO.
Dang I must be a slow typer, beat to it
I usually suggest SuSE.