Go to www.fileplanet.com and download:
Half-Life 1.1.1.0 Client (Full Client)
<A HREF="http://www.fileplanet.com/files/50000/57317.shtml" target="_new">http://www.fileplanet.com/files/50000/57317.shtml</A>
This is the latest patch to the full version of HL. I have always gotten HL to run under both version of XP, with or without the patch. Hope this helps you out.
If I hear, <b>DUDE YOUR GETTING A DELL</b>, one more time... I'll put up with it because my boss told me to.