Sharing resources across routers

Hi there
We've got a school network linked to the internet by cable modem.
Behind the modem a switch connects four routers (each with its own IP
address) to different parts of the network.

- router 1 (IP 123.456.78.001) - network dept 1
internet - switch - router 2 (IP 123.456.78.002) - network dept 2
- router 3 (IP 123.456.78.002) - network dept 3
- router 4 (IP 123.456.78.002) - network dept 4

Is it possible to share resources across these routers (eg. computer in
dept. 3 printing on printer in dept 1)? If so how? Some machines use
WinXP others WinME.

Thanks in advance

andrew.klemm