I can get the SEOmod working.

I have done the htaccess and copied and pasted the info and file into the root directory of the forums.

I still get the 404 error on my site www.seobetter.com

What should i do to fix it?

Several things :

1. Do not use iframes to display the forum !
   It's just very bad SEOwise, and it should not be this hard to alter your overall_header.html and overall_footer.html template to match the look of the rest of the site.
2. Be consistent with server settings :
   Your forum is indeed using seobetter.com as a domain, but the rest of the site is using "www.seobetter.com". You need to make up your mind and choose one or the other for both the site and the forum.
3. Also, seohelpforums/ looks like a long directory name to me. Remember that you can use virtual directories for each forum, and thus target more specifically each forum's content. And, as you more or less did, you can use keywords in the forum index url too.

Once you will have made up your mind about all this, and that you will have set your phpBB Server and Cookie settings accordingly, generate a new .htaccess, and put it where the red messages tells you to (and NOT anywhere else). Also note that you can generate an .htaccess meant to be used in the phpBB sub directory (in case it's not installed in domain's root), using the "more options" options, and then the alternate location one.

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