No answer in three days pretty much indicates that this is either not possible, or so very difficult, that it can't be readily done.
You don't have two "drives"; instead, you have two partitions on a single drive -- and that is the crux of the problem.
If you actually had two physical drives, you could disconnect the one containing XP, do a restore to the one containing Win 7, and have it installed. But with one physical drive, there is no way to do that.
Also, the image of the HP PC will contain drivers for that specific PC. Unless this PC is identical in hardware, even if you do succeed in copying the image to this PC, it is unlikely to boot due to hardware differences.
And finally, if that other HP came with Win7 preloaded, then it is not LEGAL to do what you want, because preloaded Windows systems are licensed to machines, not to people, and that copy is only legal with that machine.
I am using a dual boot system with Windows 7 and XP... XP is on C: Drive. Win 7 is on D: Drive.
