Out of interest... Does anyone have any experience with Siemens PLC's (more specifically Step 5 PLC's)?

I'm seeking some help in connecting the Step5 PLC to a PC via the AG port of the PLC or with the serial interface of the CP 521SI (in combination with the S5-100U  CPU103 I use), whatever is the easiest. I don't wanna purchase some +$1000 driver, but want to create my own (or a free one).

I also don't wanna use an existing +$1000 piece of SCADA software or whatever as I only need to grab some DW's from a certain datablock, without alarms and other bells and whistles. Idealy, I only need to run the "driver" and my own application (thus not some full blown resource hogging SCADA or HMI package).

The biggest problem is knowing the protocols (AS511?, 3964R?, RK512?). I have some very little information on AS511 protocol, but I would like to have some more info/insight...

There is very little info (virtually none) on the net about this...