I have developed some basic communication vi's for this, however, we have purchased a 3rd party serial to internet converter and just use TCP vi's with the command structure listed in the Siemens manuals for communication. It is all ASCII based and pretty easy to use. If you need further help just reply to this thread again and I can get you some more info.
If you just want to talk to an OXYMAT/ULTRAMAT via ELAN, I have a pretty well documented suite of VIs which handle the protocol over a standard serial port using VISA. You simply need a regular asynch serial port with RS-485 levels. You can get a 232 to 485 level converter, or an RS-485 interface card (NI sells several excellent RS-485 devices for PCI, USB, etc.) Email me and I'll reply back with the VIs. What version LV are you using?