the antenna i have on my pcmcia card isn't movable--just a piece of plastic that sticks out of the slot, begging to be broken off.
if you have a big problem with link quality and don't care about latency, get a repeater. dlink has one--called a wireless extender:
http://www.dlink.com/products/?pid=18 ...a little less than $100 at compusa. i used this in a situation where a client had a 3 story house. the wap was on the top floor and the bottom floor had 3% link quality. I installed the repeater in a closet between the first and second floor and it boosted the first floor's quality to 100%. the repeater works by telling it the MAC address of the wap you want it to repeat. once set up, you just plug it in to a power source and forget about it.
a cheaper option is to get an antenna. the benefit of this is you don't lose any latency (no issue of packets going from your computer to the repeater and then to the wap) the problem with an antenna is if you were to point it up, to boost the reception you say is lacking on the second floor, you would lose reception in the basement because the antennas are directional.