Welcome to Seven Forums arcanemethods,
Do you still have the Sony recovery partition?
Did you make the DVD before installing Win7RC?
You might want to save that or just not delete it. Even if you can't access it now, it can be recovered. See Access Sony Vaio Recovery Partition
, for two ways to get it working.
If you decide to sell the laptop you can put the original OS back on it.
Some OEMs may require the original OS be installed for any warranty work, check with Sony or if they don't like to answer, scan the warranty for it.
How many partitions do you have on your HD?
Just the recovery and the C:/ drive or did you add more?
Always backup your entire HD before any installation, regular backups should be part of your Disaster Recovery Plan. This is very useful if you have any problems after the install or just want to retrieve some files.
As gregrocker mentioned, did you run install from Windows 7 RC or did you boot the DVD?
It should accept Win7RC as a OS to upgrade from, unless Sony has changed something, sounds like they did.
If you haven't already, try to boot from the DVD, as described in this tutorial Clean Install with a Upgrade Windows 7 Version
Try Windows Easy Transfer - Transfer To & From Computers
, this will transfer all your user settings, you will still need to install all your programs.
You should be able to get this installed by the method in the tutorial, worst case scenario you will need to re-install Vista but, that's not likely.
Let us know how it's going, we haven't heard from many people trying the OEM upgrade and would like to know how they are working.