signal-- laptop ok, desktop not(?!)

So this is a weird one... I have a wireless router, from which I get full (good to excellent) signal strength on my laptop- sitting on top of my wooden desk- but only very low to good signal strength on my desktop- sitting on the floor below my desk. Why would this be?!
My wireless router is a DLink DI-524, my desktop (PCI) card is a DLink DWL-G510, and my laptop (miniPCI) card is an Intel PRO/Wireless 2915ABG. (You'd think the 2 dlink products would work well together!)
Even when I pull my desktop out from underneath the desk and turn it around (so there's no desk blocking it at all), the best I can get is around 55% signal strength. The last place I lived I didn't have this problem- my desktop would get a very good signal strength most of the time.
I've tried moving the desktop card antenna around to point in various directions and angles, but the most I could get was 68% (which quickly deteriorated). I checked the router and the desktop wireless card and are both set at 100% transmit power. I moved the router up a little bit so it sits at about 3' high. I've also tried changing which PCI slot the wireless card is in, in case that made a difference (very little).
Any ideas or suggestions would be helpful! Thank you all :-)
-Tamar

Well, I updated my drivers and at first I was getting a really good signal, even putting the desktop back underneath the desk. But now it's back down to a low signal strength. I don't think it's much of a heat issue, since I'm only running a P3-800MHz. I'll try running NetStumbler, though. Thanks!

I had the same problem. My notebook is curently three feet from my D-Link DWL-510 equipped PC. Network Stumbler, which I loaded after reading this thread, thank you very much, shows power of of -54 dbM and has remained constant for the past half hour. I installed new drivers from D-Link, and now the card works, but with a SN of -68 dbM. Perhaps aimee2180 needs to recheck the date of his new drivers? I was getting no signal before the new drivers, the antenna was facing the wall away from the router.