I've got a routine that is 99% complete to do this. The only missing feature is that you can't reset the post numbers (i.e. 4027 in WebBBS would be 4027 in WWWThreads). However if you are populating a new installation of WWWThreads then this is not a problem because there are no pre-existing messages for the WebBBS messages to clash with.
If you've got the time I'll send you a copy for you to finish off. My only request is that I get a mention in the header section as being the original author.
The script is pretty fast and seems to be able to convert about a message a second.
Let me know if you want to take it on.
Simon Wolf,
Webmaster,
Access All Areas
http://www.athree.com
