The tools to make models/skins for use in Source have not been made publicly available.
In other words, you can't have custom content yet. If you've seen any custom content, it was probably made from the stolen build.
Eightball, Right click Counter-strike:Source Beta and select Properties. There should be some text about 'Amount Aquired'. If it doesn't say 100% then you found the problem.
I think he should check the console first. If it tells what's missing/corrupt he should be able to get the file from someone without having to download it all over again.