Hi Davey.
All three are perfectly viable options. Is this "new guy" someone you want to have access to your existing LAN? That would be something to consider. If it's OK, then pretty much choose your option, I'd go for cheapest cost, which can still be a toss up.

1. Existing hub, add new IP address. What's that, about $5-10 a month? As long as all the protocols match, that sounds like the easiest bet.
2. Buy a router. This could eliminate the need for more than one IP from the DSL service. However, it's also probably the costliest up front.
3. NAT - sort of like turning one of your computers into a router. You'll need a second NIC in the main machine and it will always need to be on for access to the DSL.

Hope this helps