Wireless Connect Slows entire Computer Significantly

I have a d600 Latitude and for the first month or so, it connected great to both work and home's wireless routers.  However, since then, if I attempt to connect to it wirelessly, it will slow my computer so badly, I cannot even open a program.  If I turn the network card off or connect hard-wired to the router, the slow down goes away.  I am close enough to the router and get an "excellent" connection reading.  I dont know what changed, if anything, since the first month or so, but any help would be appreciated.

-MG