Nas7000

i have recently purchased a wireless router and pci adapter (both-G) i first installed my adapter about a week ago and was running fine with 600 kb/s download speeds but after i upgraded to win xp PRO from XP HOME my download speeds went down to about 200 kb/s. i have tried un-installing and re-installing my adapter....no use. i have a laptop in the house that is getting 600kb/s and full signal but im getting about 200. i dont think its spyware cause i have formatted my computer and same problem.my router model # is :WRT54G My adapter model # is:WMP54GS