WindowsXP?
You're screwed. hehehehehehe. "HAHAHAHAHAA!" Err, anyway...
if it's XP than IE is part of Windows... basically, you can't just reinstall it. IF it's not XP but something prior, then you should be able to get the newest version of IE (IE 6) and reinstall it over top. That should probably get it.
However, I'm sure you're using XP. So...
just do this:
http://www.dougknox.com/xp/tips/xp_ie_reinstall.htm
that'll reinstall it. You need the WinXP CD.