I am using Excel 2000, I have two problem, one small, one big

Small problem
I have a worksheet with just under 5000 rows and half a dozen columns. Two
of the columns contain telephone numbers. Unfortunately in the conversion
of the data to get it into a format that excel could use the leading "0"
was stripped from the phone number, how can I put the "0" back in again (I
don't have access to the original data so I can't rerun the conversion).

Big problem
This ones a little harder, I have a worksheet with around 40 telephone
number on it in one column (call this worksheet Y). I have another 10
worksheets (call these worksheet a,b,c,d etc.) which contain imported
telephone bill information (numbers called, duration, cost etc.). What I
want to do is see how often the number listed on worksheet Y appears on
each of the worksheets a, b, c, etc. Anyone tell me how??

Regards

Tim