We build a lot of websites so perhaps I can give you some advice.
If you don't know, a browser by default loads a page called index.htm (or index.php if the .htm file is not there).
You could rename your blog page to index.htm, and change the other "main page" to something else. Be sure to update your links.
THAT is a simple solution.
There are other ways to do it with what is called a .htaccess file. This hidden file can do all sorts of cool things, BUT if you don't know what you're doing, don't do it!
You can't really put a redirect on the index page, because if someone really wants to go there, they'll be sent away within a matter of seconds.
Your other option is just to market and submit the actual address
www.mysuff.com/myblog or
www.mystuff.com/myblog.htm.
In the first, just create a directory called my blog and make the name of the page index.htm. In the second, just create the page and leave it in the root directory.
Good luck!
If you need anymore help, feel free to email at the address in my signature.
Switching my website to a big cartel 
