count days excluding only sunday

Sinc you have Excel 2010
With
A1: start date.....01-Dec-2012
A2: end date.......31-Dec-2012

This regular formula returns the count of non-Sunday days in that date range:

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Note: the "1000000" code flags 0's for workdays and 1's for non-workdays.

EDITED TO INCLUDE THIS Pre-XL2010 ALTERNATIVE:
Regular formula:
A4: =SUMPRODUCT(--(WEEKDAY(ROW(INDIRECT(A1&":"&A2)))<>1))

For days to skip: 1=Sun, 2=Mon, 3=Tue, 4=Wed, 5=Thu, 6=Fri, 7=Sat

Is that something you can work with?

Another way....
Try this Array Formula which requires confirmation with Ctrl+Shift+Enter instead of just Enter.

Assuming A1= Start Date and A2=End Date, then

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Or this Regular Formula.......

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