To be honest, with four/five computers in an office, and within a 10 yard radius of the router, I wouldn't even think about a "wireless" network. An 802.11g network has a nominal data transfer speed of 54Mbps and, in practice, will be half or less of that speed. Also, I believe that with multiple wireless connections, that bandwith is "shared" by the wireless connections. While this might not be too detrimental for internet activity, for file & printer sharing in an office, the speed could be extremely slow.
Personally, I would suggest a conventional "wired" network which will run at 100Mbps, though a single laptop could be used wirelessly.
If you have ADSL broadband delivered via the phone line (as opposed to NTL/Telewest Cable) you need a combined "Wireless Router & ADSL Modem". The computers in the same room would connect directly to this and you could run a single ethernet cable to the second room where it connects to a "network switch" to provide access to the computers in the second room.