I downloaded the G.E.C.K., but every time I try to run it I get a message that says "The program can't start because SSCE5432.dll is missing from your computer." I've re-installed the program many times but get the same message. If anyone can help with this issue I'd appreciate it.

Try putting the files in the same folder as your FalloutNV.exe.

As Silver said, you must copy the files into your Fallout new vegas folder.

Should be located at: program files\Steam\Steamapps\Common\ "fallout new vegas"

Had the same problem. Had unpacked the geck in my mods folder which is a bit messy and didn't notice that this dll actually comes with the geck. so you need the program and the .dll in the fallut folder