Did a clean reinstall only to be blocked by this error code 51.
How do I get past this? Anyone else have this problem, if so, what did you do to correct it?
I would really like to get back into playing this game but have run into too many problems.

Are you running AV software? (Any but F-Secure specifically.)

By "Did a clean reinstall" did you mean you went to (My) Computer>Documents>My Games>Fallout New Vegas and deleted the ini files, (Excluding the Saves folder.) and to the game directory to delete everything in there? If not, it's not a clean install.

Could you elaborate on this? Error code 51?
Im assuming steam is giving you this error.

Take a look at this:
http://forums.steampowered.com/forums/showthread.php?t=1596741