A forum I am doing has the mod rewrite thing on it, but when a new page is made either in the topics list or in a topic the 'page 2, page 3 etc' still have the normal kinda forum urls, can bots still read them properly and go onto the other pages ok?
That's interesting. I would first check with wherever you got the mod/hack and see if anyone else reports the issue. For the most part search engines CAN and WILL find your less friendly URL's. Some search engines cannot pass querystrnig parameters which is why mod_rewrite is so popular (along with the fact that nicely named pages tend to rank better), but over time many of them have evolved to have that capability.
I am using xenobb.com which has keyword SE friendly urls built in, but when a new page is created the page number that takes you to the new url is like a normal forum type url.