I think I already know the answer, but just throwing this out there anyway...
I have done a clean install after a hardware upgrade. Before the upgrade I copied the necessary registry keys for installed games so that I didn't have to install and then patch them again. Worked great for most games except BF2. WHen I try and play it comes up with an error telling me my CD key is invalid. My BF2 box with the serial is in storage and I can't be arsed sifting through three tonnes of stuff to get to the box that has the box in it. I have checked the reg entry and it seems to have the cd key in it under HKLOCALMACHINE\SOFTWARE\Electronic Arts\EA Games\Battlefield 2\ergc The CD key is preceded by x93920 then xxxxxxblahblah.
Anyone know of a workaround to get the CD key that is already in there to work?

Thanks

install bf2 then copy ur backup folder over top of the fresh install- wen installing use the key that is located in the registry file if u can get the complete key from it.

I hope that makes sense

Unfortunately the key as it is in the registy is encypted...it is not the key in plain text.