WRT54G users

[KitKat]

When I hooked up my router to 3 computers I still had to run the network wizard but it gave me the option of setting up the network to allow shared files between computers. If you don't want each computer to have access to each other don't setup the shared files in the network wizard

[THEKATZ*{MEOW}*]

That's a good point Kit.  Windows does a good job at protecting your files.  Though the new software comming out with Linksys and Netgear are actually taking this function over.  So how ever you choose, look for that option.  Preferably, use the software that came with the device.  Like Kit states, you may still need to run the Windows Home and Office network wizzard on each computer depending on the hardware's software that came with your router.