I have a Linksys WRT54G but th9ose are fairly old. Although i have had one for years for XBL without issues.
Are you using a standard wireless Xbox adapter with it? If not i would also get the Linksys WGA54G to go with it.
I used that combo for many years without issues from about 100 foot away from the router. But really the speed of your internet service will impact the online play more than what router you choose. (upload speed is crucial when hosting games such as Rainbow Six Vegas)