If the problem still exists when you use the cord optical mouse, then it has nothing to do with the wireless mouse. The chance is you prolly have some spyware or even virus infection. Try running adware and spyware S&D and see if it fix the problem.
Your temp is fine, 45 C is lower than normal, and overheating wouldn't cause mouse problem anyway I think...
First Built Computer:
Antec Plus1080(SOHO File Server)+430w
Intel P4-3.0E 1M Cache
Asus P4P800-Dlx i865PE,800FSB Dual DDR400
WD 120G-8MB Buffer
LG 16X DVD
LG GSA4082B DVDRW 8X +/- Black
ATI Rdeon 9600XT 128M
512MB DDR PC3200