If you are getting a PC with Vista, double check to make sure it has the free Windows 7 upgrade.

If its a 'name' branded machine (HP, Lenovo, Toshiba, Dell, etc), then this is pretty much a given that it will have it, as the large manufacturers have already updated their product lines to include the upgrade coupon.

If its a custom built or 'white box' machine - you'll need to check, as Vista can be purchased either with or without the Win 7 upgrade coupon by resellers. If the reseller is trying to do the box as cheap as possible they may supply the PC without the coupon.

Ironically I've been getting a lot of questions at work around this from our customers (resellers) - my job is looking after the MS business at an IT distribution company.

Cheers,
S.