Will need to purchase the PC to L connection converter kit...Lennox part# 96L78.
The issue with this kit is that it uses a 9pin serial port to connect to your laptop, so will need to go to Radio Shack and purchase a RS232 to USB converter. Most new laptops do not have a 9pin or 25 pin serial port.
This is a must if you want to access the older M1-IMC boards...not really sure cause I have not tried it, but the new M2-IMC (Prodigy) boards have the USB port in addition to the RS485 phone jack connection, so a flash drive loaded with all the settings can be dumped in during commissioning. So you might just get away with a USB line to your laptop on the Prodigy, never tried it.
I just always keep my converter in my laptop bag and whether a M1 or M2 series I just use that. Have an assortment of fittings and converters for all the systems I may run into.
As for pricing, can not get into that here, but your looking less than hundred bucks on the Lennox converter and less than fifty on the Radio Shack thing-a-ma-jig.
Tried to make my own converter in the early days, but did not work, when I got the Lennox converter, it had a little more to it than just going from a RS485 to the RS232, circuit board and components, pretty proprietary. But so is every other companies..York Simplicity, etc.