I do not believe you will be able to install ColdFusion 10 and have access to the serial number for CF8. The serial numbers are version specific. Even if you install CF8, I'm pretty sure it will force you to enter that key during the installer process. If you skip your way through that by entering the developer/trial mode I do not believe it will recognize that you had a key once it is up and running.
You may be able to get the key from where you ordered it. I order all my coldfusions from the Adobe store, and I can get to any serial number through that, unless I ordered a physical copy. For those, my account history says that the serial number was included with the physical media.
Regarding moving the key, assuming you have it, I believe what you want to do is legit, uninstall from the old server, install to the new server, and reuse the same key.
Thanks for the info on everything.
There is nowhere that Adobe stores it within the filesystem for retrieval? I figured it would at least be in the registry.
If not, I guess I will have to ask my supervisor about obtaining the key though our order history, etc. (I really hope they didn't buy a phsyical copy and if so someone has it still, ha!)
How about open ColdFusion8\lib\license.properties file, or restore file from backup case CF8 uninstalled, check details pertaining to sn= ?
As Carl mentioned if you have ColdFusion 8 directories left in the installation folder then you can check the files which mentioned and opened with Notepad and you will get the ColdFusion 8 serial key but that won't work with ColdFusion 10. Again if you don't find that folder, can you please let me know any order number or any other details so I can help you with that. Please send me a private msg with that information if you have.