internet going slow on vista 64bit help

[wes2k9]

hi ive just installed my wireless n usb and signal is at full strength.Loading internet explorer and accessing pages take ages lol i feel like im back to 56kb modem.
i use xp on a laptop and it runs fast using a 802.11g card,i have norton anti virus on my new pc if that could have anything to do with it?

if anyone has any experience with this issue or could just help i would much appreciate it

thanks

 

[wes2k9]

gpu ati 4890
cpu phenom II 720be
corsair ddr3 ram 1600 mhz
asus crosshair III mobo
1tb seagate hdd

is the avasi software as good as norton 360?