Avant, which uses the Windows shdocvw.dll core for rendering
http://www.avantbrowser.com/
K-Meleon, which uses the Gecko rendering engine
http://kmeleon.sourceforge.net/wiki/FAQ
Patch the kernel with KernelEx and run Firefox or IE or Opera
http://sourceforge.net/projects/kernelex/
Or compile any Linux browser against Cygwin
http://www.cygwin.com/
Or use a lightweight Linux like Puppy from a LiveCD (yes, I know that this begs the question)
http://puppylinux.org/
q
NB: Don't blithely install a current Linux distro on an old machine. Most will bring the machine to its knees - there is no magic that makes Linux multitasking inherently faster than Windows multitasking, and you'll find after benchmarking that WinXP makes better use of your old PC than all but the most austere Linux distros. Unfortunately, to get good performance with WinXP still requires you to jettison a lot of extraneous services. Microsoft won't help you do this, but there *is* a distro floating in TPB that has already done it for you. Don't ask, don't tell.