In my shop I've seen a few brands/models if you try to run a Vista to Win7 upgrade it will fail.

If this is happening, back up your data (usually everything is stored in your personal folder), do a clean install (run your win updates and install an anti-virus program like Microsoft Security Essentials / free), then copy your data back over.

A good clean install is much better, this ensures that you don't have clutter and junk left behind from Vista even if the upgrade to Win7 would work.

A last note, since you bought the Windows 7 discs, when you clean install Windows 7 be sure to leave the HP restore partition alone (the restore partitions are only about 2-4GB). This way if you decide to sell it later, you can just hit a key on boot up and factory restore it back to Vista and still keep your Windows 7 / bought disc/serial number.