If your serious about porting over, then I would consider looking at D3Forum module, this is far more secure, newbb has a few issues, and apparently has flaws which allow people to view private area's, which could be detrimental to your website regarding the data protection act.
D3Forums Module - Download
It might not look as fancy, but you can play with the templates and make it look really special.
There is also Newbbex
http://xoops.instant-zero.com/
Goog luck and have fun with XOOPS
Tom
http://bassmanthemes.com
http://www.xoopslance.com