I have started playing around with modding Windows XP... and i am have done some pretty cool things to my OS (courtesy of the labor of others.)
Here are a couple of sites...
This site has a utility, and a bunch of visual styles for XP, it allows you to change the way your start bar, start button, and menu look. Right now my start bar is cherry red, as are the menus and buttons... (if you know XP you know your limited usually to blue silver and nasty green) THere are hundreds of visual style skins at this site too. However, the app that makes all this possible is only shareware, so if you like it, you should buy it.
If your a power user like me, you never have enough space for all your windows, even if your running dual monitors. If you have ever had fun playing around in Xwindows on a LINUX box, you probably noted how cool it is to have transparent windows... well.. now you can have it in XP. Download Glass2K and the VB dll's that help it run, and presto chango, you can set your windows, start bar, button, menu's to varying degrees of transparency (Visible, 0-9 settins)
I am currently watching Norton System Works 2003 install, right behind the window I am typing.. I can litlerally see the scroll bar moving... very cool.
If you have never used it before, you will be wowed.. (if you use MSN Messenger, Yahoo Messenger, IRC, ICQ, or AIM, or all of them![img]http://www.**********.com/iB_html/non-cgi/emoticons/wink.gif[/img] Trillian binds them together in one nice neat package, no longer a need to have 5 different contact lists open to talk to people on different networks. Trillian imports them all and makes them work together... very cool... and lots of cool features. It can also be skinned like Winamp.
If you haven't done it yet, download the new media player, it will dock on your startbar so you don't waste space on your usable desktop area.
I will leave registery editing of Prefetch and other stuff out... I don't want to be responsible for some over ambitious people tanking their registry... (not good when this happens![img]http://www.**********.com/iB_html/non-cgi/emoticons/wink.gif[/img]
BTW, it is reccomended that only people with moster systems go for this stuff, while you probably won't notice much of a performance impact on older comptuers that can run XP, you might, but the newer systems will shrudge this stuff off like a sneeze.
Have fun.. make your desktops look more like you, and have a blast.
(Oh, there is a cool Longhorn Addon bar at xptheme.org too, if you don't know what longhorn is, it's the nextgen os from microsoft... It is a pretty cool bar, but I don't use it currently... not in my 'style'.)