XP isn't known for such on good hardware. You should do the usual tests by removing the case cover to see if there is a heat issue. If the lockups subside, then you talk to the machine's supplier.
Also, since SYM(antec) is a possible issue, remove it and try Free AVG for a while from http://www.grisoft.com Let me be clear that I have no cure for Symantec's 2004 software.
We have recently upgraded 8 of our office computers to WIN XP Version 2002 SP1 and MS Office 2003. These are AMD Athlon XP 2000+, 1.67 GHz, 512 RAM built computers. 2 of these computers are experiencing random freezes. Going into Event Viewer and System Error Records, we see the same DCOM error on both machines. Following the HELP & SUPPORT instructions to find the vendor/program causing the error, we have tracked down the registry file SymWSCSvc.CLASS. We believe this may have something to do with Symantec. We are running Norton 2004 Anti-Virus, but we can't find anything to tell us what this file is. Any thoughts would be appreciated. Thank you.