Forum OpenACS Q&A: Response to Attempting to call a win32 dll from ACS running on Linux

The main (only?) advantage of going with XML-RPC is the fact that you already have the client and server libraries for whatever languages you want to use (client on Tcl and C or VB (?) on the server, in your case). You could design a lighter weight protocol specifically for this use, but it would take so much time that it probably doesn't make business sense.