Routing IPtables setup

[Knut Ole]

I'm trying to set up my iptable for the following setup:
-one router (A) which is connected to ISP.
-second router (B) which acts as a repeater bridge due to distance to first router.
-my three computers (macbookpro, ubuntu, xp)

I want to both access internet from all computers thru router B to A to ISP - and use router B as LAN for the three computers (for fileexchange).

router B is setup with dd-wrt rep/bridge mode. but how should my routes be?

thanks for reading,
k