Bank Account Register

Hi all, Please CC me on any reply - I get the digest :) I am working on a project where I need to implement something that most resembles a checkbook register, where I am tracking pre-paid hours bought vs. hours used on-site. I am getting a bit stuck on the best structure for the mysql table, and would like some suggestions. In the end, I need to be able to run a report where by date it displays hours purchased, and hours used like in a check register:

DATE    DESC.                   BAL.
2/23/04 Purchased 10 hours      10hrs. remaining
2/24/04 Job 2 used 5 hours       5hrs. remaining
2/24/04 Purchased 20 hours      25hrs. remaining

Like so... Would it be best to have 1 table with a field for transaction type and keep all the ins and outs in one table, or have two tables one where I track purchased hours and the other where I track used hours? Thanks, Rogue