cpu change

Hello. Today I changed my CPU. I had AMD Palomino 1900+ XP(1600mhz) and I changed it with Sempron 2500+. I didn't do format or Windows reinstall. When I turned on comp,comp recognized new hardware,but CPU was called AMD K7. In hardware properties processor is called: AMD Athlon(tm) 1.47 Ghz,and nothing else. In BIOS its the same.
It seems this cpu isnt working at its proper perfomance... What shall I do? Windows reinstall or smth else? Thanks.




oO?