Hi Charles,
When I had my LXD75 mount I guided very well using PHD [free].
http://www.stark-labs.com/Since the LXD75 does not have a direct guide port on the mount you will need to guide through the extra port on the handbox using the ASCOM platform and driver.
You can download the ASCOM platform here:
http://ascom-standards.org/Downloads/Index.htmAfter you have loaded the ASCOM platform go to the stark-labs site and download and install the LXD75 driver:
http://www.stark-labs.com/phdguiding.htmlDownload the "Meade ASCOM driver from Jonathan that actually works" below the image of the PHD display.
You now have all the drivers for guiding. PHD should show a selection for "Meade Classic and Autostar I" under the mount menu.
The only thing left is to connect from the PC to the handbox.
On mine I made a connector to go from the PC RS232 port to the handbox. I think you can get a USB adapter from Shoestring Astronomy:
http://www.shoestringastronomy.com/You might send them an e-mail and ask what you need, they are very helpful. Tell them you need to connect from USB to the LXD75 handbox.
This is all from memory, hope it helps. Someone else might have some pointers too.
Brent