Forum move SEO and clean url's or not recommendation

[jpietrowiak]

Hi All,
I had already setup clean URLS for my forum. However I have noticed some potential problems using this and what like to know what others think. I have moved over to VBulletin from another forum software as well as decided to put it on a subdomain instead. So another words All my old pages links in the forum will need to be reindexed by search engines.
My question is.

1. Is this going to be a big rank killer since the pages moved to another location?

2. If it is and I use url rewrites and decide to rename a forum then all the topics within the forum page links also change. So would this be a big hit once again by doing so?

3. I assume I could use 301 redirect for old pages but will doing the above still kill my long time standing in the search engines?

4. Also is having clean URLS worth taking the hit if there is much of a hit with the search engines?

Thanks for everyones help

Jamey