Great to see you getting the system stable. Just one thing though, i think your temps are wrong. The cpu is always hotter than the system, from what ive seen anyways. The reason for this is the heatsink is cooled by air blown onto it by the fan. That air is taken from within the system, so its blowing warm air onto it. I could be wrong though.
To answer your questions...
First, make sure the temperatures are right for cpu because if its not then you have reached the limit of the cooler. Try taking a reading before playing a game, then play a game for 5 mins and then take another reading straight away. The one thats risen the most is the cpu temp.
Next if your sure about your temps being ok, change the cpu voltage to 1.75 volts and try a higher multiplier until the system is unstable. I would say dont go above 1.8 volts but thats your choice... Im not sure what problem windows is having though, maybe someone else can help here...
Also i REALLY recommend running prime95 for an hour or more to make sure its 100% stable
2100xp @ 2300mhz (200x11.5 @ 1.9v)
Epox 8RDA3+ Nforce 2 ultra 400
2x512mb pc3200
ATI 9700 pro
3DMARK 2K1 = 16,000