it sounds like a pre built pc from a shop that comes infested with lots of shit offers like norton etc...
if im right, you wont actually have a cd as the HD originally in it will have a partition with a kind of image of windows 7 there already, incase anything goes wrong.
windows vista upwards are really shit with upgrades and as soon as something changes on the computer it will start getting bitchy.
surely you can just install the second hard drive and run two. would need a SATA cable most likely.
sorry if that's totally wrong but it's how im interpreting it