I have a 1999 ford taurus It has a radio with no cassette player I was wondering if it would be possible to change out with a factory radio with one that has a cassette

Shouldn't be a problem as long as you don't get one for the Mach system. I'm not sure the standard tape player would have the proper connections for the Mach system. I'm assuming you want a stock system with a tape player rather than an aftermarket system. If you want aftermarket, then you will need an adapter plate for the instrument cluster and a bypass harness for the Rear Control Unit (RCU) in the trunk.

-Rod

Use crutchfield.com to find out what you need to do the install. Excellent info on that site, and there stuff usually comes with great directions for installation.