Here you go - copy the attached system hive back to the original location - overwrite the one that is in there.
Windows should be able to start and install the new device drivers
If you still have an issue- then either 7 doesn't have the required drivers in it's repository - or there is something wrong with the way you connected up your new mobo and ram.
Glad I did that - found out how to do it now.
Bit fiddly getting permisisions your registry - did it from winpe instead.