It could be that your router is operating in 802.11b mode, which is a very poor communication method, for reasons I'll not bore you with here.
Also, B-mode is a maximum of 11Mb/s throughput.
So, login to your router, and choose 'G-mode Only'. This has much less re-transmission & collisions, has a 54Mb/s max throughput, and should cover any laptop you have as long as it is not 5+ years old.
EDIT: Blaymay, I didn't suggest he switch frequencies, I suggested he switch modes.
He is suffereing slow-down, and has an existing connection, so making sure 802.11b is not chosen (as any one device on the network in B-mode, will force THE WHOLE ACCESS POINT to B-mode.)
Bet I'm making way more $$$ than your nasty @ss.