use the same edition of your copy of the windows you own .then you can use your key normally,

remember the same edition

sp1 or sp2 or media center or home edition(sp1-sp2)

you can use any disc. the product key number is the only thing that matters because you have to register it at some point.

All the CD’s are exactly the same. If you use someone else’s disc with that serial it should work perfectly fine.

No it’s not illegal, when you buy a new license you’re basically buying that Product Key.

The only thing that would be different about the cds is if it’s Home or Pro.