Yes it is possible. However you'll be editing the core files to do this, so make sure you log everything you do and put the log somewhere where you will see it before you update to the next version when it comes out.
Here's what you need to know.
Mysql. You need to add cells to the customer info table. You can do this with either phpadmin or whatever front end admin program you have for mysql.
Remember when you create the cell you'll need to set the type of cell, whether it's text, or numbers, etc.
Then with php, you'll need to add a field to the form and by looking at the other fields you'll should be able to figure out the code.
I'll have to look at the files to tell you which ones you need to edit, but I'm going to leave soon. I'll try to work on this more later today unless someone else comes up with a quickie.
Also, check the downloads section to see if someone has already come up with a mod for what you need.
John Patrick
A Zen Cart Advocate!