Wireless speed drops after a few minutes after boot

I've been having some difficulty with my wireless connection settings. I''m having difficulty even getting around 80kbs from my wireless. I did a speed test from my PC and it came to around 0.8mb, and in real world apps download is limited to that download speed and gaming is impossible, I get massive lag spiked, even though that speed is normally fine for gaming.

Here's the strange part, when I restart my computer, right after the restart if I do a speedtest it will hit the normal 6-7mbs, and gaming will be fine. Several minutes after it reverts to the same ****!

My laptop sits right next to my PC, and if running a speed test from it reveals no loss of speed, I'm getting regular speeds of 6-8mbs. I'm confused!?? I've also disabled firewall.

My PC spec is

Windows Vista 64bit
2*2gb OCZ 800mhz
Asus P5Q-E
Q6600@3.00ghz

Wireless card is: Zonet ZEW1602, I can't even go the website it gives me a warning!
Wiress router: Lynksis WRTG

Any help would be greatly appreciated.

With wireless, reception and interference must always be the prime suspects.

See if you can detect any neighbouring wireless and move to a channel 5 stops from the strongest.

I assume you have looked at MTU setting in the router (1500 is default, try lowering in increments of 10).

Also try turning off DOS (Denial of Service) protection in the router.