Multiple domain names

oops, they're all getting indexed...

[AnonyMouse]

I recently launched a site, but dithered over what url to use - an old one that had a holding page, or a new one with a better ring to it.

I decided to use the older url, hoping that because it had been around for awhile it would get into the SERPS more quickly.

However, I also pointed several new urls at the same hosting account, so that they point somewhere - although I didn't submit the urls to any search engines.

But now both the old url and the new urls are being spidered, and I'm worried about duplicate content flags going up! To make things more confusing, Google is indexing the new url faster than the old one (which had been static for years).

I'd appreciate comments on what I can do to prevent the dupe content from being spidered (301's?), and which url I should keep as the "real" one.