You might be better off posting this question in the Google forum, as it's a question which relates more directly to Google rather than Domain Names as a whole.
I can't see how basic forwarding - be it via frames or through a redirect - would cause problems for your ranking. Some of the more Google-savvy users will be able to provide more reliable information though!
If you've not done so already, have a look through the site search [webmasterworld.com] as it's quite likely this question will have been asked before!
R.
