In the off change both your router and your wireless card support it, try the "a" band, it operates in a different RF bandwidth that the b & g bands. Note that most access points/wireless routers do not support both a and b/g, you would have had to pay a few extra $$ to get one that does.

Also, try different channels, cover the entire range such as try 1, 6 and 11 and see if that makes a difference. As others have said, in an apartment or condo building, neighbors' cordless phones can have an affect.