The documentation (user manual) of that motherboard will tell the upgrade possibilities. If you can find a downloadable version, please repost your question with a link to that manual in our http://forums.cnet.com/pc-hardware-forum/
Kees
Computer details:
-Processor: Intel(R) Pentium(R) 4 CPU 1.80GHZ
-Speed : 1794, 32bit
-L2 Cache size : 512 B
-Processor ID : X86 Family 15 Model 2 stepping 7
-Ram size : 2G
-Hard disk size : 160GB
-Windows 7
-Mother board : i845G-W83627HF
-Video controller : Intel(R) 82845G/GL/GE/PE/GV Graphic controller

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic