Business & farm

What I am gathering from your facts are the following:

1. You have a business organized as a C corporation which files a form 1120
2. The C corporation had a line of business which consisted of a bookkeeping business
3. The C corporation sold this line of business
4. The C corporation is continuing on in existence
5. If the above is accurate you have the following:
1. The buyer and seller must complete a form 8594 for the sale of the "assets".  This form must be attached to the C corporation tax return.  The IRS will also compare this to the buyer's return so you need to make sure this form is completed together and both parties are reporting the same amounts in each asset class.
2. This form will provide guidance on how to allocate the sales proceeds to the various classes of property on the form.  I would assume most of your purchase price would be allocated to classes VI and VII which are Section 197 assets.
3. The gain for the C corporation would be the sales price less your basis in the assets sold; which in this case I assume is "0" or close to it depending if any other tangible property was sold as well
4. The C corporation would also need to complete form 6252 to report the initial sale and the subsequent payments received
5. The interest received would just be recorded as interest income the same as would bank interest income

This can be a fairly complicated area and highly scrutinized by the IRS.  Depending on the $$ involved you may want to consult with a tax professional.