But the most obvious thing is Mismatched RAM.
Assuming that it is DDR1 RAM you should be using pairs of RAM in Color Matched Sockets and ideally install as much as the M'Board can carry. I have several 1.7 GIG P4's running quite nicely with 2 GIG of RAM Installed. If you have one of the HTT CPU's and the M'Board fully supports that you should get even better performance.
The other thing to check is the HDD for possible failures so get yourself a copy of the Ultimate Boot CD available here from the Listed download site not the yellow add.
http://www.ultimatebootcd.com/download.html
Then test the RAM while it all may be all perfectly OK if it's from different Makers or Speeds there is quite likely to be Timing Issues which causes the system to Lock Up. While ideally 1 GIG is OK with XP it's better to have more if the M'Board can carry it and it's much better to have identical RAM. But no matter what you should read the M'Board Manual from Gigabyte to see what you can use with this M'Board.
After you test the RAM remember to test the rest of the Hardware as well. Also if the system runs perfectly well off the Ultimate Boot CD and continues to fall over when you start Windows you need to do a Repair Install of Windows by following the directions here
http://support.microsoft.com/kb/315341
If you have a M$ Branded Install Disc follow the directions in Method 2 but after you have finished that you will need to reinstall any Hot Fixes & Service Packs that where released after the Install Disc was made. ;)
Col