As you say, you have to get another PC-Card wireless adapter. This can work. You'll just disable your old one and use your new one.
The best solution though would be to replace your integrated one, but I know from experience that Toshiba, HP, IBM, and Compaq do not allow you to do this. Toshiba doesn't allow you to access the integrated card, and HP and Compaq make you buy the card through them.
Dell is the only major manufacturer which gives people the ability and indeed encourages their customers to upgrade not only their wireless but also to put in Bluetooth, RAM, change the keyboard, and so forth.
The advantage of upgrading the internal card is that it has a quicker response when coming out of standby, uses less power, and the antenna can't be snapped off.
Hi,
I have a Toshiba Centrino laptop (M35 series) that came with integrated 802.11b wireless. It works fine for the most part. However, I seem to be getting a lot of interference in many places - others' wireless work while mine doesn't. I am thinking of maybe buying a new wireless card, a 802.11g, which will hopefully work better. Is this the best solution? And if so, will there be any conflicts or problems that I might need to deal with (having two wireless cards)? Thanks!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic