NW 6 sp5 with Dhcp running, BM 3.7 on NW 6 Sp5. HP 4000M switch w/VLAN. DSL
w/5 static IP's all being used.

What I have is very sound well running network. But our President has
decided to rent out office space in our building and included in the lease
Internet access for their PC's. This small company has 6 workstations and
shares files with one another on a peer to peer setup. My contact is
concerned with security and so am I. I will have no control over their
Workstations (anti virus, spybot, etc..)

Is their away to isolated their network from ours without buying more

Separate segments? VLAN's? and how much would this help?

Any info or suggestions would be greatly appreciated.