With any wireless network there is bound to be some lag depending on the distance from the wireless card to the access point/router. Lag is also caused by interference. Certain cordless phones microwaves and other electronics can cause problems. (Don’t forget the material the walls are made out of)
How far will the ps2 be from the accesspoint/router?
linksys makes nice wireless routers. easy to use and set up. as for how the G preform i really havent read many reviews or know anybody who used one. Hopefully someone can help you out with that