Which router and Adapter should I buy???(for restaurant use)

I did try the LINKSYS WRT54G Wireless-G and NETGEAR RangeMax 240 Wireless router. I can't receive any signal from both of them. For some reason, the router have to be setup at the front of the restaurant and the office room is at the back of the restaurant ( around 200ft ) ( the office was using the NETGEAR WPN111 USB 2.0 RangeMax Wireless Adapter ) What i guess is maybe the restaurant's wall is made by some different material like fire resistant wall. So which wireless router and adapter should i buy???

The problem proably lies with the LT. Are you using a PCMCI card in the LT or the built in? The built in's are poor. You could run a Plenum rated cat5 through the ceiling.
If you convinced you want wireless. Try a USR5450 AP with a USR5410 . I use this setup. 5450 has duel Hi Gain antennas. I'm able to cover my house on lo power. But not near the distance you are doing (50' 4 walls on Lo power).

Go the wired, cheaper. 500' for cat5e plunm, around $60. Then find some one to terminate it for you.

Or mount the AP in the center of the room and allow patrons to use it.