Looking at our watson data, we have several customers who encountered a generic "setup failed" message when installing the .Net Framework.
When we look at the installation logs, regtlbv12.exe is failing. Regtlbv12.exe simply registers tlb files. It will fail if the registry is locked which could happen for numerous reasons.
A customer on the newsgroup found a workaround which Aaron Stebner has documented at:
Hopefully this will help you get around regtlbv12.exe failures when installing VS 2005.