((I had the video card in for a few months and never had this problem until I rebuilt my pc. The parts I added were the CPU, mobo and PSU.))
when you added the MB, did you get rid of all the drivers from the old MB, usually when you add a new MB, it's always best to re-format the HD, then do a clean install of your operating system and then install all the drivers for your new MB etc. IF that has already been done, try doing what " jmoore2001" recommended. I run a Athlon XP 2500 overclocked to Athlon XP 3200 and my cpu temps are 38C and 40 C at load. Make sure the heatsink and fan are mounted the correct way on the cpu, if not you may damage your cpu. Also make sure to put a THIN layer of thermal paste also.
Just some things I could think of. Good LUCK....