Can we buy a tv convertor box that will work with Comcast Cable?

I have comcast cable and internet. With comcast internet, we brought a modem from Office Max because we got sick of renting the one from comcast. It works fine. Ealier last summer, we were forced by Comcast to rent the digital cable box from them. I was wondering, first, if we can buy our own tv convertor box instead of renting the one from comcast? If we can, who is selling them and can we use the coupon from the government to buy it? Thanks in advance for your help.

You don't need to get their box.
For example, there are Tivos with Cable cards, or you can buy a PC with a cable card slot and use it as a PVR, or if you don't care about premiums channels, and PC with a digital TV tuner will work. You may even find DVD recorders that support digital cable.
BestBuy and other do sell cable set-top boxes and most new HDTVs have tuners that support analog and digital (unencrypted) cable.

They will force you to use there equipment. That's why I just get TV of the antenna. I will buy my converter and no monthly drain of my money.

Cable encrypts their signal and quite often changes the encryption algorithm to prevent people from gaining access to their cash cow.

Simply put, you will need to rent their converter box - or do like I do for most of the TV's in the house = just watch basic cable.