My mom just purchased a new compaq cq56-115dx laptop that came with windows 7 home premium. I wiped it out and installed xp since that is what she is used to. Now I have an older compaq presario v5305vm laptop on the way (came with xp media center edition, but vista drivers are available) and I was wondering if I could use the license on her laptop with my older one since she has no plans on using windows 7.
If you want the actual license to use it on your other computer, it depends. Since it's an OEM license you are most likely only permitted to use it on the machine you bought it with. There are exceptions to this, however, such as in Germany, where you are permitted by law to use an OEM license on a different machine or sell OEM licenses separately, provided you don't use it on the original hardware any longer. If you just want a key to activate, use the one provided on the COA. You'll be able to activate it fine, it probably just won't be legally licensed.
Looks like you're totally confusing OEM COA and SLP keys: With COA key (the one from the new laptop's sticker) OP can activate whatever computer he wants, at least one time via Internet, it doesn't need any SLIC and digital certificate, only inet or phone, and SLP key was wiped along with wiped Win7... can be found on this forum though but as you said is useless on the older machine without bios mod or slic emulator.
Sorry, I wasn't clear on that. I only wanted the COA Key on the bottom of the laptop. So I guess I should just try it and see. I have restore dvds for the new laptop, but I know they won't work on the old one.