Ouch - Google says 15,328 404 Not Found

This doesnt look good even for a newby like me, even I can see that I may have a large problem on my hands.

I recently replaced a phpbb forum with 110,000 posts with vbulletin and vbSEO. Horray no more p*rn bots

vBulletin 3.6.8
vBSEO Google/Yahoo Sitemap Generator v2.1

The phpbb was located at Website Hosting - Mysite.com . Unfortunately due to many phpbb modifications, I was unable to convert the forum and save all the posts to the newly installed vBulletin (so I was told - I dont know if this is true). This would cause the existing phpbb to move to Website Hosting - Mysite.com and the fresh vbulletin will be installed Website Hosting - Mysite.com

This is obviously the problem with all of the 404 errors.

My question would be how would you handle this situation? and is this affecting my se ranking?

Thanks for your time.

Probably the best you can do is try to setup some custom htaccess directs to send the old formats (phpBB) to your new forum's homepage.

Any idea as to where I could get assistance in figureing out how to accomplish this?

Impex should be able to pull the posts and threads over.. I havd a massively modified setup on phpbb before I went to vB, and all of the posts and threads were imported fine, the URLs were different, but that's obviously going to be the case.

What Impex can't pull over is anything non-standard... who told you that you wouldn't be able to import your threads and posts?

yeah, you CAN impex from phpbb to vb. Obviously your customizations won't carry over, but your users, threads and posts should

Is it posibile to import the posts, but only the posts from the old forum to an already runing vBulletin?

A sub forum should be created, and that subforum should contain all the OLD sub-forums and posts. Is it possibile?