Please use the edit feature, no reason to triple-post in less than 30 minutes from the first....
The rough prices are like $150 for a yearly license, maybe a little less. iPB used to have a perpetual license in that you bought it and you got all upgrades to it for live (was like $160). But they got rid of it.
I personally feel SMF is the best of the free-ones; however, it's a matter of personal opinion. You can see all 3 in action at their respective sites ( www.phpbb.com || www.simplemachines.org || getvanilla.com ). They all have similar features, and others are better at some things than the rest. But it's all personal preference. No-one can say definitively that anything is better than the rest.
if you're running windows XP home, I wouldn't put forum software on it (except for testing of course). If you want to start a community (like this) you really need a webserver (see my post above for some sites) that will take care of you. Servage is really good (I was with them for a year or so, HostRocket is good too, was with them for a year). Or you can go and pay the $100 for an unmanaged dedicated server, or go with www.mosso.com and use any server you want (IIS or Apache) from one system. That's $100 a month but is pretty cool.
The reason you can't run a community from home is because of the bandwidth that would be involved. Most ISPs won't allow you to run a webhost from your home.
If you really need hosting, IM me (see my links under my Avatar <--- ) and I'll get back to you later today when I'm home from school (4.5 hours from now).