Actually, Great Plains will still post a transaction date of 2030 if your batch date is setup properly, if you are using Batch Dates as your posting (vs transaction date). Typically, when you create a batch, you enter the transaction into today's date for the batch, but then manually type in the transaction date.
What I would recommend to your user's is the following date shortcuts:
If you are in the current month and date, you do not need to enter the entire date ie if today is 10/22/2003. If I am in a date field and want my date to be 10/15/2003, just type in 15 and tab off.
If you are in the current year and want to change the month and day, type in 1115 to make the date 11/15/2003. You only need to enter the year when it is different from the current year.