Internet Explorer

I don't think it's even possible to fully uninstall IE in XP or Vista. Without IE you can't get Windows Update anymore, some web pages will not work properly, and like the above, above poster said, some programs will not function properly. If you do manage to find a way to fully uninstall IE, I really would not recommend it. I don't see why simply not using it is such a huge issue.

Btw, if you're using XP there's a way to have a minimal trace of IE on your computer but it won't completely be gone. (See below)

 Spoiler

If you want a minimal trace of IE on your machine, go into the Add or Remove Programs control panel and click on "Add/Remove Windows Components," on the left side of the screen. Scroll down to Internet Explorer and uncheck it. (It will say the option is 0KB in size; this is normal, since, as described above, you aren't deleting any actual files, just making them invisible as a web browsing system.) After this, IE won't show up in any menus or on your desktop, and it won't ever launch as a web browser. (You can still use IE Tab if you need IE's rendering system. To reinstall IE, just reverse the process above and recheck the box.) Source