Pam, aren't you in for a treat! You will have to accomodate for a few differences between the two systems, and yes, I (and many others who may not have taken the time to post) have ran across these nuances as well.
As far as the "BILL" (and/or "SHIP") field, you will have to modify that field on the form, the easiest thing to do for me was just to create separate fields for each letter. Reason being is that I found that forms print slightly different on various printer models.
The PO form header issue may be fielded better by someone else, as it's been awhile since I looked at that... thought there's a setting in there someplace, or you could just modify that field on the form I guess. Good luck!