Seperating networks

[Steven C. Peterson]

I currently use a Linux box running Clark Connect to run my network, 
this box supply's a modified Linksys wrt54g to provide my wireless services
that said most of my devices run on the wireless, the wrt54g pulls dhcp 
provided by the Linux box, I am unaware of what software
Clark connect uses to run the dhcp server.
 
My question is Along with my devices and my roommates devices i have 
some other people who pay me to provide inter net to them (We co-op in 
to a pair of bonded t1 lines), i would like to separate my network from 
every body else's, (I.E. I do not want them to see my printers and 
shared folders, nor do i want to see theirs.)

Any suggestions other than putting another router in place?

Steve