You could run a script upon startup that searched for any birthdays in the next 7 days, and if any record are found you are left in the found set, otherwise it will just show all records, or where ever you want to start from.
So your scritp would be along the lines of:
Allow User Abort [ off ]
Set Error Capture [ on ]
Go to Layout [ Client Details ]
Enter Find Mode  // untick the Pause option
Set Field [ CLIENTS:: DateOfBirth ; Get ( CurrentDate ) & "..." & Get ( CurrentDate ) + 7 ]
Perform Find 
# Assess Result
If [ get ( FoundCount ) > 0 ]
Show Custom Dialog [ These clients have a birthday in the next week ]
Show All Records
Then you need to set this script to run when you open the database, go 'File > File Options...' and then under the options for 'When opening this file' slick on the 'Specify' button next to 'Perform Script' and from the Specify Script dialog select the script above.
I hope this helps.