Redirect, Hurting Site Rank

On my site http://www.example.com the same pages are displayed for differnt URLs could this be hurting my site rank?

e.g.

http://www.example.com
http://example.com
http://www.example.com/site/
http://example.com/site/

The four URLs above all go to the same location

I have a redirect set up on example.com to redirect to example.com/site using php depending on the client it will be example.com/site or example.com/other.

I also have example.com/site set to change the url to www.example.com/site using php again.

I hope that makes sense so far, my question is, is that hurting my site ranking? (looking at my google results it does appear to be the case) So how can I make my site more friendly to search engines?

Normally I wouldn't bump a topic but seeing as someone posted in every other topic but this one, it got lost.

Hmmm I was wondering the same

anyone can help us?