Hi everybody
I just wanted to know how to convert Hijri date in a column in Excel2007 into Gregorian?

This REALLY depends on what is REALLY in that cell. Dealing with dates is a bit of magic trick because very seldom do we see what is really in that cell, rather we see a "specific visual formatting" of the hidden number in the cell Excel uses to identify dates to itself.

I would think if the value is truly a standard Excel value formatted to display as Hijri, then you could simply apply a different (gregorian) date format and it would display properly.

So, read here and see if this helps you:
How to enter and use Hijri date in Microsoft Excel 2003

If not, post up a sample workbook showing your actual data in these date cells and we'll take a look.