Changing URL for blog, what do I do w/Google?

Im switching myblog to mymainsite.com/blog from a separate URL I was running it on.

It has been indexed, verified, etc. on Google. Do I need to submit a new URL on Google webmaster tools, a new sitemap, etc.?

And am I gonna lose my indexes?

The indexes will be lost and the new links will be detected by google as duplicates. Try to redirect all the links to new links. I've done something like this in .htaccess (if the old site is on apache and you can change it). Hopefully you can do it.

Redirect 301 old_link new_link

good luck

Wow. Is there a step by step on this somewhere???

I'm REALLY wanting to avoid duplicate content :/

Just search on google for .htaccess 301 redirect tutorial
You'll fine plenty of resources. But this is only if your old blog is hosted on some apache server and you have access to your blog directory and can change files there. I assumed your blog in some php script

If your blog is hosted on blogger, blogspot or something similar I don't know how to do it, I hope there is a way...

Yeah, my blog is hosted on the same server as my website. Thanks for the heads up.

Wow. Just gotdone reading. Thats a heck of a process.

So theres no hope of simply changing the phpadmin settings to point the wordpress software back to .com/blog?

Thats how I orignially got my blog from .com/blog to the new URL.

I don't think so. I assume you imported the content of a blog from a different url. If someone will go on the old url the new one will still not be involved.
In conclusion you need something in the old url to redirect all the call to the new url. I know that .htaccess doc is complicated, but what you need is very simple to do.

For the beginning I would try to put the following line in .htaccess, and replace old_link and new_link with some existent link you have. Then if it's working for one try putting some * in the redirected urls....

Redirect 301 old_link new_link

Read this:
http://forums.seochat.com/seo-help-general-chat-16/301-redirecting-208054.html
This might be helpful to you.

You definitely want to use 301 redirects, I did a case study on this. The real benefit of 301 redirects is Google will transfer all PageRank authority linking to the old pages to the new ones.