I Love Trillian Pro
This thing is grrrrreat! Like GAIM for Linux and Fire for MacOS X, Trillian is an multiple-protocol instant messaging client that subsumes America On-Line Instant Messenger (AOL-IM or AIM), Yahoo! Instant Messenger (YIM), Mirabilis ICQ, and MSN Messenger. Great plug-ins, great clients, no more weird crap with screen savers shutting off (leading to overnight burn-in) or GDI resource overloads (leading to thrashing and inability to pop open the one more Explorer, Internet Explorer, or Outlook Express window I need). And best of all, fewer bluescreens!
If yew dknot have it already, I highly recommend it! It's the best $30 I have yet to spend (but soon will).
The XP Silver skin is actually reminiscent of MacOS X.