Why does my laptop have much better reception than any of my desktops?

Ok, people, please tell me what the heck I'm missing here. I live in a house with a bunch of students and we're all connected to the same router. All of our laptops (including mine) can pick up our router's signal very strongly and can detect approx 15-20 other networks around the area... But why is it that my three desktops, in the same room as my laptop, can only pick up our network very weakly and not detect a single other network? My destops have a linksys wireless g PCI, d-link wireless G usb and I just bought last week a Linksys wireless N USB which only upgrades my "very weak" to "weak"

My desktops have such a weak signal that they disconnect every 2 minutes. I don't understand... why do laptops have so much more range? I need at least one of my desktops to have the same range as my laptop.

Conceivably because the laptops can be positioned better for reception than the more bulky desktops -- which have large chunks of metal shielding them from the signal.

USB is usually less useful than PCI but try using the extension cable which usually comes with USB sticks, see if goes from weak to less weak.

N only works better than G if both ends are N (sorry to sound like an equation)

Ok, so I did some reading, which is what I should of done to begin with, instead of listening to the stupid retards at the stores. Turns out that wireless N cards do NOT give you better coverage or range than a wireless G. Only gives you faster speeds (if connected to a wireless N router).

So why does my laptop have better signal that my USB wireless N? Is it possible that the Built in Antenna is absolutely huge?