My games crash new Dell PC w/ Pentium-D

I have a new Dell Optiplex GX620, Pentium-D, 2.8 Ghz, 1GB RAM, XP-Pro.
Display adapter is integrated Intel 82945G chipset. Direct-X 9.0c. I've
installed two games (Rise of Nations, Age of Empires) I used on my previous
system. Both games cause system crash (reboot) 20 to 90 seconds after
gameplay starts. Video trailers and menus at start of games run OK; problem
occurs only after start of gameplay. Microsoft Game Advisor indicates both
games are compatible with my system. All drivers are latest shown on Dell
and Intel websites. System passes DXDIAG tests. Dell can't (won't) help.
My initial thought was video hardware, but I'm now wondering about the
Pentium-D. Anyone have any ideas?
--
Brian