XML-RPC calls

Hello,
I’m just trying to write a little XML-RPC client for putting new entries into my wordpress-weblog. Now I am using the Meta Weblog API, which works fine, except for one problem: I can’t figure out, how to set the category. It always put’s the new entry into the 1:General. So far, I tried to put:
category: 2, ‘int’
or
category: ‘xmlrpctest’,’string’
into the struct and neither works. Since I also used w.bloggar before and could easily post into categories with that, I wonder, what I am missing here.
Maybe someone of you friendly folks around here, know how to do that? 🙂
Any help, any hint, even a: “You’re dumb, it works this way” would be much appreciated.
Dominik