I am looking to phase out one domain and move to another. I was wondering what the best way of doing this was without completely distroying any search rankings I have built to date?

Using htaccess 301 rediret will move the pr over etc

I don't really think there is a "Perfect" way to accomplish this. Yes, as Simon said you can do a 301 redirect to the new domain. Although, in my experience that just informs the search engine and forwards the visitor to the new site. So, you will keep your current rankings until Google sees that you are redirecting to a new domain. Then, you will drop in rankings for a while before you pick it back up. PageRank, does not transfer just because you do a 301 redirect.

I would recommend changing the content, and making some SEO improvements to the "NEW" domain.

Definitely 301 the pages.
Don't make any other changes at the same time (tempting though it is) - give the bots no reason to be confused. Just move it.
If you can, make the move gradually over a few months, ie each day change a few pages and all the internal links that point to them to the new domain.
Obviously this is easiest if the site is setup programmatically.
If it is all hard coded you'll be living in hell for a while...

Hope it helps
Lea
~ first post - hi guys!

Hi Lea! Always great to have other opinions!!

I transferred the whole site. Changed the design a little and reorganized the content. It flows better now. I then 301ed it to the wrong it the wrong website. (You have to be a L33T programmer to do that.) I fixed the .htaccess but firefox kept being redirected to the wrong site. I restarted Firefox and everything. Was stumped for a couple of hours before I finally restarted my computer and the oddity passed.