Linksys Wireless Router :: Slow Internet Speed With WRT160N?

I've recently purchased a WRT160N router, and I'm using it in conjunction with a WMP54G wireless PCI card. I've set the router up to my requirements, and can get a stable wireless connection.. but internet speed seems excessively slow. While I'm able to get up to around 4MB/s transferring files over the network, running speed tests, it consecutively shows my download speed to sit around 400KB/s, whereas I'm able to get a steady 1.1MB/s on another desktop that is wired. Disabling the LAN adapter on that computer, and connecting via wireless, brings down the speed that that computer is able to get to around 400KB/s as well. Hence, I don't think it's my wireless cards, but something to do with the router itself.I'm also experiencing lag spike issues in online games, which I can only attribute to the current wireless setup, because I've previously had no issues with it. All relevant ports are forwarded, so that is not an issue.After doing some Googling on the subject, someone had suggested running SpeedGuide's TCP Optimizer, and changing the RWIN - I ran it, and set it to the 'optimal' settings, and after a reboot the wireless seemed fine - I was getting just a tad under what I should (about 950KB/s).. but after a short while, it just went back to 400KB/s. After further investigation, it seems that Vista automatically changes that RWIN value to optimize network traffic.. but I never had this issue with my old wireless gear, so I can only assume that the way Vista is reacting is based on the way the router is interacting with it.