For the past 1,5 years the entrance page of my website was the main forum index. This is done through .htaccess. Now I would like to change the entrance page of my website to my IIP entrance page, but I'm affraid that this change will harm my Google listing/numer of indexed page.

My current forum index has a pagerank of 5 and the page contains a lot of keywords for my site, while the IIP has a pagerank of 0 and much less keywords.

Any advice appreciated

If you haven't done so yet:
Create an account at http://www.digitalpoint.com/tools/keywords/ and put in your relavent keywords and find out your google rank on those keywords.

Then make a change and observe your ranking the next 2-3 weeks.

thanks for the link Anno, I found it helpful already .