You can read this in Bugtracker comments too:
I think it's not a good idea to add frames. They're outdated.
Did you ever press refresh on a website which is build on frames? It's horrible!
If your clients want to use Google Sites, they (or you) could also register a Google Apps account to have Google Sites with your own domain.
Google Apps Standard: http://www.google.com/apps/intl/en/group/index.html
Click on Get started, this version of Google Apps is free, but limited to 50 user accounts per domain.