It's important to know what type of RAM you have. Many dealers sell systems with 400 Mhz bus mobo and install 266 Mhz RAM. If you are going to buy a system, these are the two most important parts; mobo bus speed and RAM speed. Don't buy if the RAM are slower than the bus speed, and check if the mobo have OC capabilities.
Software wise, it is always more important to initially make sure to know what hardware you have.
Asus P4P800 SE
Intel P4 3.2 Gig 1024 Meg PC3200 cas latency 2.5
RAID 0 2-36.7 Gig SATA WD 10,000 RPM
200 Gig WD ATI ALL-IN-WONDER 9600XT
6500 Kb bandwith Internet Connection