First of all: Consider what you’re doing with Windows. If you’re playing the latest games, don’t expect to be able to play all of them with Linux. WINE and WineX attempt to emulate Windows programs (the latter isn’t free, but does add DirextX support), but don’t count on any of them working. That being said, Half-Life apparently runs under WINE (I don’t know, and I don’t want to saddle this poor little P3 450 with it). Q3A, UT, and some other games have been ported, including I believe UT2K3.
If you still want to switch over, SuSE does an admirable job of autodetecting and autoconfiguring all of your hardware. SuSE is the first version of Linux I’ve run that I could actually get my sound card to run under. It also runs KDE, which is quite Windows-like, only prettier and faster.
Photoshop: There’s the GIMP (GNU Image Manipulation Program), which I have found to be more than adequate for my image manipulation needs.
Office: There’s StarOffice and OpenOffice, and there are commercial plugins (CrossOver from Codeweavers) to support MS Office.
IE: Get Mozilla Firebird. Hell, get it even if you stick with Windows. It’s fast, highly configurable, and the little search bar next to the address bar can be configured to search on engines other than Google. I currently have the Cambridge Dictionary, Webtender, and FOLDOC (Free Online Dictionary of Computing) on mine.
Winamp: xmms is about the same as Winamp 2. It might not (yet) have the super-fancy skins, but it handles a wide range of audio file formats from the get-go, and many more can be added via plugins.
Outlook: Mozilla Thunderbird. 'nuff said.
AIM: There’s gaim, kopete, and everybuddy. All of these support more than just the AIM protocol, including Yahoo!, MSN, ICQ, IRC, and Jabber.
p2p apps: Bittorrent, eDonkey, and gnutella are all well supported. Freshmeat.net is a good source of these programs.
One caveat with SuSE: Many programs are not included in the default install (but are on the CD’s) that you may need when compiling programs distributed by source code. These include gcc, make, and nasm. SuSE uses RPM files on its CDs and FTP sites. Think of these as auto-installers. You have only to open one of these files under KDE and click on “Install with YAST” (Yet Another Setup Tool) and it’ll either install or tell you about the conflicts, which are usually other packages you need.
A General Linux Caveat: Learn the basic commands for use with the command-line, just in case something goes wrong and you can’t get into the X Window System. SuSE installs w3m, a text-based browser, by default, so you can figure out what the hell you did and get your desktop back.
Hope that helps.