Spotty, slow connection - is it my pci card?

I am running Vista 64 on a new build.

I have tried two separate routers, both broadcasting in g (no n router yet).

I installed this wireless card:

ENCORE ENLWI-N IEEE 802.11b/g, IEEE 802.11n Draft 2.0 PCI 2.3 Wireless Adapter Up to 300Mbps Data Rates 64/128-bits WEP Encryption WPA, WPA2 WPA-PSK, WPA2-PSK - Retail

I have tried both the drivers from the CD and the latest Ralink 64-bit drivers.

In both cases here is what happens:

Signal strength on each antenna between 10 - 30%

Link quality between 40 - 60%

Looking at the Windows wireless signal strength meter, I'm at 1 - 2 bars.

Internet connection is spotty and sub 56k speeds at best, non-existent at worst (with no change in the above stats).

4 other laptops in the apartment can get signal (again, at 1 - 2 bars on the Windows signal strength meter) and operate at a normal speed (if not very fast, still fast enough to download large files in reasonable times). 2 of the laptops are running Vista 32 and two are running XP.

I should also mention I can put a laptop in the exact same spot as the desktop and still get working wireless, so I know the signal can reach the location (the broadcast is 2 floors down).

I am thinking it must be the card. I have tried uninstalling reinstalling, everything. I'm very much a networking amateur but I can't for the life of me figure out whats going on.

I'm running out of my 30 day return policy, should I just send it back?

There are certainly different things I could buy to try and improve the signal (and I think I still will) but what I'm worried about is the card. Do the 4 other laptops really have substantially better wireless cards than this one (with three external antennas?)