Airport express and Linksys WRT54G

Hello,

I just moved close to a neighbor who uses an airport express router
for wireless internet and itunes on his apple computer. I myself have
a Linksys WRT54G and a desktop PC. With authorization from my
neighbor, I have been using his wireless link for low MB activities
(emails, Google earth, browsing, etc.). The problem is that I can't
connect to internet from my office because the reception is too poor
or inexistant. The only solution for now is using my girlfriend's
laptop from the kitchen (best reception where i live)!!! Obviously, i
can do this for ever.

My question is whether i can use the Linksys to act as a bridge AND-OR
an amplifier of the signal? Take note that i don't know much about
computers, but if someone was to send me some detailed information,
that would be perfect. If i can't use my linksys, what are the best-
cheapest options instead of suscribing to my ISP?

thanks for all your helful advice.