Hi Scott
There are still issues with some older software and hardware, so check on the manufactures web sites to see if the hardware and software you want to use is suitable, or can be upgraded to work with Vista.
My recommendation if you have the room is keep your old computer and XP and just add the new computer with Vista, (You can use the same monitor and keyboard by just adding a switch box) that way if you do find something that wont work with Vista you can still use it on your old machine. (Network them together and you will be able to transfer files as if it was one machine, you can also use your old machine as an additional firewall when connecting to the net)

To All
NEVER connect to the internet without some form of security installed, and make sure you keep it up to date (There are many good quality free apps out there) or you will have problems. (When you see the tears in the customer’s eyes, when you tell them that you have not been able to retrieve any of their treasured photos, after a virus has totally trashed their machine, you will understand why security is important)

Finally
BACKUP, BACKUP, BACKUP, BACKUP, NO EXCUSES don’t wait for a disaster to happen. (Its no good shutting the stable door after the horse has bolted)
Hope this helps

Bill