Here's how I handled it in GM 6.5 dbase version...
Create a field for holding the birhtdates. In my case, I created ubirthday.

Here is the filter script:
DtoS(contact2->ubirthday) > ' ' .AND. (DOBINDAYS(Contact2->ubirthday)<8)

This returns all birthdays coming up in the next 7 days. Using this expression, it would be very easy to find them, or create a AP to print a birthday letter or email.