A VLAN is just than, a virtual lan, instead of a physically segregated network, you have a logically separate network. It isnt so much a case of you 'sending' traffic, it more a case of if you have 4 ports assigned to the same vlan, you have 4 ports that can be communicated across. They wont 'leak'. If you assign vlan x to ports 1, 2, 3 and 4, vlan y to ports 9, 10, 11 and 12; then correctly addressed devices can communicate with each other within their vlan, and their vlan alone.
However, as this is all done at layer 2, if you do want to get traffic off these vlans you will need to route it.
If, as it sounds, you just want to 'kick off' certain pc's from your LAN, so they can soley communicate with each other and nothing else, then set a vlan up on your switch, assign the offending pc's ports to the configured vlan and advised them of their network addressing.
You can get away with leaving them as they are if statically assigned, but that doesnt prevent any one from patching them into your ports and communicating with your kit, give them a new subnet and you'll be better protected.
If they use/access physically remote resources, you'll need to look at trunking and vtp domains etc.
How reliable are they? 5000+ users, 40+ vlan's, 3 DMZ's, 4 firewalls... we're pretty happy with them.