I have no clue why. I just installed for the first time, using Windows XP. I've opened Limewire, and my computer simply reboots. Is this a known issue???

No, that's not a usaul known issue.....could have several causes.
What LW version do you have and where did you get it from?? From the official website?:
http://www.limewire.com/
What Java version do you have installed? The newest (1.5.0_07) installed using the JRE offline installer (before installing LW) and rebooted?:
http://java.sun.com/j2se/1.5.0/download.jsp
Have you recently checked your system for any trojans/worms/viruses using some up-to-date software??
http://www.lavasoftusa.com/software/adaware/(free)

http://www.grisoft.com(good free AVG)

http://www.ewido.com(free trial which can still be used and updated after the period has ended)

http://www.ccleaner.com/download/(free)

Spybot - Search & Destroy (FREE)

When was the last time that you have defragmented your HDD??

__________________

"Never Argue With An Idiot. They Will Drag You Down To Their Level, Then Beat You With Experience"

Hmm.. I just d/led limewire 4.12.3 from download.com/cnet.
1.5.0_06-b05 is my Java build.
I scan every 3 or so days with spybot, adaware, and AVG - everything's clean.
I defrag every week or two, last time was 2 days ago.

This is very, very strange. I'm definately knowlegeable with computers and rarely run into an issue I can't figure out by doing a little research... but this one has me totally stumped. I'm wondering if some of the extra Windows services I disabled could have anything to do with this, but I don't see which one(s) would be required for limewire to run.

Okay, my advise at this point would be to uninstall LW and your Java completely. Then go to the official LW website and download the newest version of it (4.12.6). Do the same with the Java (using the link in my post above). Choose the JRE offline installer. Install Java, reboot and then try to install LW. If the problem re-occures, try the following. Right click the LW icon on your deskto and go to Properties>Compatibility......change the compatibility mode to Windows NT or Windows 2000 (try NT first, then the latter if it didn't work out).
Should that not do the trick, uninstall LW again, reboot in Save Mode and install LW again.
By the way, try Ewido,....you will be surprised.....I was after scanning first with AdAware and SpyBot, just to find a couple hundreds more with Ewido...

__________________

"Never Argue With An Idiot. They Will Drag You Down To Their Level, Then Beat You With Experience"

Cool. Will try tonight and post results tomorrow.

Will also try the other spyware scanner you reccommended.