Hi
I don’t think this will affect your ranking, I am sure you are familiar with the process.
No matter what, changing your domain name will affect your search engine rankings, largely because each search engine responds differently to such changes, but you can substantially limit the damage done. Google has taken the lead as usual in dealing with URLs that change and will quickly index the new file with virtually no interruption if you follow some fairly straightforward procedures. AllTheWeb quickly followed suit. Unfortunately, the procedures described below do not work in the same way on the other major search engines.
The critical element in successful url redirecting or domain forwarding is taking the time to make sure that ALL links to your old page from directories and other websites are updated. That step must be done. Unfortunately, it is the most difficult step, as many links may be on sites that are neglected or even abandoned.
Google has published guidelines on changing your URLs. See, Google Information for Webmasters : "Once your new site is live, you may wish to place a permanent redirect (using a '301' code in HTTP headers) on your old site to inform visitors and search engines that your site has moved."
hope this helps ..:)