I have a Toshiba Satellite P205-S7402 laptop, and it supports 802.11b and g at present. I want to use 802.11n as well - can I just swap out the wireless card with a new PCI card?
Yes, it would upgrade to 802.11n. But with laptops it isn't very easy to switch a PCI card. You could use a USB wireless adapter or a different kind of pluggable solution (PCMCIA or what it is called these days).