OP -- suggest you take a trip over to batlabs.com and read up on their primer for programming radios. Most of the people above gave you some terrible suggestions.
The CM300 uses a similar looking cable to the unit that does 90% of the other mobile radios in the Motorola fleet, but for the CM300/PM400 platform, you must use a box that switches the pinouts, or use a different cable. The CM300/PM400 platform is unique. I am not familiar with the Maxton cables - so I can' t tell you what you've got.
Yes, as mentioned by SteveC, you can most certainly use a windows based computer for any of the current radios using CPS. If you're using an aftermarket cable setup that runs off a USB plug, you're going to have to play around a bit with the port settings to make sure it works right. It sounds like you've already loaded the aftermarket USB drivers, but make sure the CPS software is pointing to that comm port.
Good luck to you.
Current Commercial series CPS software for the CM300 is: 05.18
Current Professional series CPS for the HT1250 is: 06.12.09
Your "Tuner" software will not program a codeplug or frequencies. The tuner software is to change power levels, frequency tuning ( to align a radio that is off freq), and other settings that used to require a tuning stick back in the day.