Wireless Adapter Unstable?

So here's my situation:

I built a new computer, running Vista HP 64 SP1, and bought a Linksys WMP54G wireless adapter (PCI).

When I do a ping test (search -> "cmd" -> "ping -t google.com") I get anywhere from 300-2000ms ping. While playing online games, my ping is around 300-700 (rendering them unplayable).
If I go into device manager and change ANY setting, the ping test drops to ~90ms (what I used to get on an older pc) and in game drops to ~40 (also normal for older pc).
After 2-5 minutes, the ping on both the test and game skyrocket. I did this back and forth for an hour now and no setting that I change in device manager permanently helps my ping.

Any help with getting my ping back to normal would be greatly greatly appreciated.