Quake3 (yes 3) Punkbuster Crashing

Well I decided to have a nostalgia trip last night and dusted off my copy (well folder more precisely) of quake3 for a quick blast around the servers.

This is what happened:

Quake3 offline/hosting = absolutely stable
Quake3 online without Punkbuster = absolutely stable (although not many servers support no PB)
Quake3 online with Punkbuster after installing 1.32 update afresh = goes to spectator mode and says "please update PB to latest version" blah blah

Right ... so I update Punkbuster and get onto the servers (any) and everything is fine for a min or so - I'm not booted back to spectator mode after 20 seconds - no problems there - but ... the system nips up (crashes/locks up i.e. NO BSOD) and I'm forced to reboot !!!

I had this same problem a while back on a completely different system - but here's the spec in case it helps:

CPU: A64 3200
mobo: Gigabyte NF3-250gb
RAM: 2 * 512MB Corsair 3500 (cas 2)
HDD: SCSI U320 36GB & SATA 160GB
GFX: ATI 9800Pro

Please note that every other game runs flawlessly for hours on end at maximum details as does Quake3 without PB enabled.

Any help much appreciated :)