here is my suggestion.
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1. decide whether you want to use a software solution for your multiboxing (ie: keyclone/ahk). if no software, go to next post.

2. if you are going with keyclone (my bias is showing here )... try starting with just 5 characters on 3 machines, saving you a bit of money until you get the hang of it.

3. go to the local best buy and buy your machines (ask for exact specs if needed)

4. buy a netgear firewall router (if you don't already have a NAT firewall router)

5. plug your computers into the router and boot each

6. turn off windows firewall on your machines (no need while gaming behind a hardware firewall)

7. install wow on each machine and log in

8. download and activate keyclone on each machine

9. on each machine, add your wows to keyclone (ask if more needed.. should auto-add by default)

10. on keyclone, type in the ip and port (located in the keyclone title bar) of your main keyclone box and hit enter or the 'connect' button

11. you are now multi-boxing. setup your follow and assist macros as needed

if you need more, we can chat via phone. i also have friends in the washdc metro area if need be (you should be ok without it)