Windows 7 Windows 7 product key

Right.....I bought a brand new pc a week ago (delivery was already delayed by 2 weeks). It was running windows 7 home premium. Straight out of the box there were disk errors. Wouldnt load up anything. Tried everything but to no avail. As i had already had to wait 2 weeks for it to be delivered, i decided to try and run vista 64bit, which i had installed on my previous laptop. The installation went fine and it is now up and running on vista. Now, i've obviously got the genuine windows 7 product key sticker on my system, but i dont have any windows 7 discs. If i was able to get hold of another windows 7 disc, could i just use my code?? (my dad has an IT department at work which he may be able to borrow one from). Also would it have to be windows 7 home premium?? Could i not use my 'home premium' key with 'ultimate'??