Windows Network Problem

We recently upgraded to the new D-Link Dir-655 as we have 2 computers that are connected wireless. Both are within 30 feet of the router and are running Vista.

One connects fine with a Belkin PCI wireless card. The other has a Linksys Wireless-G PCI card and doesn't run so well.

At best, the Belkin one gets 54 mbps while the other gets 11 Mbps. When a laptop is connected to the network, the Linksys one drops down to 1Mbps, while the laptop gets around 20 Mbps until the router is rebooted.

I have tried changing the channel, but that doesn't do anything. When I tried playing with the Transmission rate, it gives the Belkin 54 Mbps while the Linksys simply can't connect.

Can anyone help me out here? All the drivers and firmware are up to date, and I really don't want to drop a bunch of money on a new PCI Wireless card.