Migrating / Duplicating existing content to new URL

I read a bit in the forums about bringing on a new URL, but i’m not sure what i’ve read is what i should do for my situation. I currently have a primary URL (www.ernharth.com) with all the permalinks, etc. Since that was established, I was able to aquire a more attractive URL name for the brand (www.vigilantinvestor.com), and i subsuquently changed to the name of the blog to match that new URL. That new URL name is set to merely mirror the original URL, hence when someone enters via vigilantinvestor.com, their address bar does not provide them with permanlinks for my posts. As well, all feeds continue to be projected from my original ernharth.com feed.

Ideally i’d like the new url to have all future permalinks for my posts without killing the existing permalinks that are out their on the net. Just the same, it’d be nice if the old posts’ permalink structure could also be duplicated at my new URL that fits the brand.

I also don’t think I want to divide traffic among two databases so my stats are consolidated, etc. Is that something to worry about? Or should i just copy my old database to a new SQL database, modify it to the new URL, and link to that through a new installation of WP hosted at my new URL?

What is the best way to go about this? I really don’t want to screw this up, or for that matter, confuse my traffic by making the wrong logistical choice.

Any advice / help is greatly appreciated.

Thanks in advance for your two cents!