Sorry for the late reply.

I have been trying to call functions_newpost.php through WSDL for the past two days. It is not going that well. There is something wrong that I am not able to fix. Zend Studio does generate WSDL properly from vBulletin's PHP file using the comments you guys provided above your functions (excellent... well done). But referencing the service in visual studio gives me unexpected errors in the app.config file, which I am not able to fix. There are too many variables that I have to take in account. So I had to abandon this idea.

So, unfortunatly I feel obligated to duplicate what 'build_new_post' does in .NET code. In order to do that I registered all the tables in vBulletin's DB which get updated after posting a thread on the forum. And I've got a few questions about that:

1) table 'adminlog'; what is this table used for? Is is updated necessarily by posting a thread on the forum?
2) table 'cronlog'; what is this table used for? Is is updated necessarily by posting a thread on the forum?
3) table 'moderatorlog'; what is this table used for? Is is updated necessarily by posting a thread on the forum?
4) table 'phrase'; what is this table used for? Is is updated necessarily by posting a thread on the forum?
5) table 'pmtext'; what is this table used for? Is is updated necessarily by posting a thread on the forum?
6) table 'post' (well this one is obvious... so no questions);
7) table 'posthash'; what is this table used for? Is is updated necessarily by posting a thread on the forum?
8) table 'postlog'; what is this table used for? Is is updated necessarily by posting a thread on the forum?
9) table 'rsslog'; what is this table used for? Is is updated necessarily by posting a thread on the forum?
10) table 'template'; what is this table used for? Is is updated necessarily by posting a thread on the forum?
11) table 'thread' (well this one is obvious... so no questions);
12) table 'threadread' (well this one is obvious... so no questions);
13) table 'threadviews' (well this one is obvious... so no questions);

Thank you very much in advance for answering.

Seeing as everybody knows exactly what they are doing we have gone with RSS feeds.

The .NET application now creates RSS files. Goes without saying that this works like a charm (as long as you don't need very complicated things like polls and such).