Windows Media Player was the most common MP3 player on Windows computers (and its a good chance your PC computer already has a copy installed). Here is a step-by-step for playing the MP3 CDs in your computer with the program 'Windows Media Player' on your PC computer:
Insert the MP3 CD into your CDROM drive in your computer
Go to the lower left of your screen and choose: START MENU>PROGRAMS>WINDOWS MEDIA PLAYER
Once Windows Media Player is open choose the menu: FILE > OPEN (or Control-O)
Navigate to your CD drive (which is most likely in your D: drive) - to do this you may have to go to the Desktop: My Computer: D:
You should now see the contents of the MP3 - it may be just a single folder -- if so, open the folder and then inside the folder there should be a long list of .MP3 files
Click on any MP3 file and click OPEN
The file should then start playing (just make sure your speakers are turned up) and you're set!