brobins75,
Lets break this up and address this piece by piece.
1) The RS125 will output NMEA 0183 if the RS125 GPS is version 2.3 or later. I don't know how to tell the version but if your RS125 is reasonably new then it is probably v2.3
2) The RS125 will output Seatalk too. The choice between SeaTalk & NMEA is done by wiring the output cable for either mode. The wiring choices are described here:
http://www.raymarine.com/GetFile.aspx?fileId=783&categoryId=3
3) Raymarine instrument transducers are designed to work with the corresponding Raymarine instruments. The transducers are powered by the instrument head, and the output from the transducer is in a form only understood by the instrument head. For example, the speed transducer outputs a series of contact closures (two per paddle wheel revolution). The Speed instrument processes these contact closures to produce the speed display. The temp function is a variable resistance and the instrument head reads that resistance to determine the temp. The instrument head then manufactures the SeaTalk sentence from the interpreted transducer signals. The signals from the transducers are just that; signals, not data.
4) Raymarine autopilots require a control head be wired to the corepack to function.
What to do:
1) If you have v2.3 of the RS125, wire the output of the RS125 as shown in the picture. You can make the rs232/db9 cable yourself, you don't have to buy the Raymarine cable. Connect the yellow wire to pin 2 of the db9, and connect the ground or screen to pin 5 of the DB9. That's it, only 2 connections required.
2) You didn't mention if you had any serial ports on your mini computer but if you do, plug the db9 into an available serial port.
3) If you don't have a serial port, you'll have to obtain a USB to serial adapter. There are several brands but I have had the best luck with the Keyspan 19HS serial to USB adapter. Install the Keyspan drivers, plug the DB9 into the adapter, and insert the adapters USB plug into an available USB port.
4) Use Device Manager on your PC to determine the com port the Keyspan adapter is emulating. The com port should be listed under "Ports (COM & LPT) within Device Manager.
5) Once you know the com port, start your charting program and configure it to use the corresponding com port. Set the com port for 4800 baud, 8 none & 1.
6) Your charting program should start displaying position data.
If you have an older RS125 that does not output NMEA 0183, then the ballgame changes. You WILL need the E85001 Raymarine SeaTallk to NMEA convertor box.
1) Bring the RS 125 cable to the E85001 Box. If there are no other Seatalk instruments you will have to supply +12V DC to the 85001 box as shown.
2) You can make the serial cable for your PC. Same as above.
3) Connect the serial cable to your PC as above.
Hope this helps.