lag problem with new wireless router

My parents recently upgraded from our hardwired switch to a Linksys wrt54gs wireless router. Once it was installed and working, i did notice a slower load time when I use the internet. Tonight is the first time I played Halo pc in a while and since the router was installed. However, I was very dissappointed to find that I had a HUGE lag problem that made it unplayable.
Now I also noticed that if I download something, my download speed only maxes at about 170 kbps. that's a HUGE difference from the speed i got on my wired switch! I use to get at least 300kbps.
Note: I have road runner business class so my speed is high end. I've used speednet.com to test speed and I had an upload rate of over 10mbps whereas my connection now only allows about 4mbps.

So, my question is what can I do to make my connection speed faster and resolve this speed problem!
Is there something that wasn't setup right?
Also: I am only using one computer on that router as of these tests/experiences with slow connectivity. both of my desktops have CAT5 cables connected to the router, so no interference with any signals.

I am most grateful to any response!