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.

At the risk of being simplistic, if you are accustomed to performance via ethernet wireless will always seem much worse.