This is exactly what I've been trying for the last week. If you could tell me how to pull an entire individual thread by id, including attached image and display it completely on a non-forum page, I'll be forever in your debt. I've been able to display latest activity and new threads in specific forums, but not with attached image because I can't get the enclosure tag working. I've tried magpie and simplepie as parsers - only thing I haven't tried is the beta2 of simplepie that supports any type of enclosure as I only found out about it today.
In the meantime I've decided to change angle and use wordpress to compose the articles and link them to a vbulletin thread for comments. I've found a lot of posts and plugins on here. If anyone could point me towards the best/most appropriate solution using wordpress, again, I'd be very grateful.