Average If Statement (Excel 2003)

I am trying to find the formula for averaging cells in column B if the data
in Ais (a specific criteria). I've tried some formulas in the threads
related to average, but nothing seems to work.

If A1:A110 equals 01
Then Average B1:B110 (cells related to the criteria in A1:A110)

When using formulas, should cells have a specific format? Because there is
text involved, I set the cell format to general. Do you suggest differently?
Also, I'm working with data that I exported from a Microsoft Access 2007
database (SQL) but I'm using Excel 2003. Will this cause a problem?