Help Picking Out a Wirless Card for PC?

Hopefully you guys can help me, because I don't know squat about this. I just built a new PC and I want to give my old one to my mom to use (ASUS P4P800, P4 2.4GHz, Windows XP Home). This will be put in a room just off the living room in their house. In my niece's bedroom (which is one room away) she has a Linksys router (I believe it's a WRT54G). My niece has agreed to set everything up herself because she doesn't want anyone messing with her computer. Fine. Less headaches for me.

My dilemma is in choosing a wireless card for the PC. What do I need for this? I started looking around but the terminology has me completely lost. There will be a wall between the room the PC is in and my niece's router. Will that be an issue? Any help would be greatly appreciated.

Thanks

I'm thinking of getting this Edimax card. It gets some good reviews.