I've got my i7 rig planned out and ready to build. I've already bought some of the parts My plan is to get windows 7 when the rc arrives in May. I'm looking for a rough prediction for how much it should cost so I can figure it into my budget.
The RC will not cost you anything and as of the Beta it only allowed upgrades from Vista SP1. Backup your data and get ready for a full install if you are looking to move to Windows 7. The RC will be good for about a year generally before you have to upgrade to the release version. It is possible that MS will put in an XP to Windows 7 migration path but I wouldn't count on it at this point.