Add numbers to column based on order number change

I have an excel spreadsheet that looks like the following.

Order No. Order Date Ordered By Ordered By Company Ordered For Ordered For Company Product Code, Revision Version
100739 11/1/2013 Scott, Kimberly Virtus James Delbert Browning, - Edward Jones 8020, 0113 B258
100739 11/1/2013 Scott, Kimberly Virtus James Delbert Browning, - Edward Jones 8417, 0613 B4

100740 11/1/2013 Butler, Jessica Virtus Troy Lawrence Young, - First Citizens Securities Corp 8020, 0113 B258
100740 11/1/2013 Butler, Jessica Virtus Troy Lawrence Young, - First Citizens Securities Corp 8415, 0613 B4

100746 11/1/2013 Salerno, RJ Virtus John O'Neil, - Merrill Lynch VIR003, 1
100746 11/1/2013 Salerno, RJ Virtus John O'Neil, - Merrill Lynch VIR008, 0112
100746 11/1/2013 Salerno, RJ Virtus John O'Neil, - Merrill Lynch VIR021, 1

I am creating a macro that will insert two new columns at the beginning of the spreadsheet named,(Order and Lines).
I need to find a way to automatically fill in a "1" in the first cell of the order? and then "1" on each other line items in the "Lines" field.

Result would be:
Order Lines Order No. Order Date Ordered By Ordered By Company Ordered For Ordered For Company Product Code, Revision Version
1 100739 11/1/2013 Scott, Kimberly Virtus James Delbert Browning, - Edward Jones 8020, 0113 B258
1 100739 11/1/2013 Scott, Kimberly Virtus James Delbert Browning, - Edward Jones 8417, 0613 B4

1 100740 11/1/2013 Butler, Jessica Virtus Troy Lawrence Young, - First Citizens Securities Corp 8020, 0113 B258
1 100740 11/1/2013 Butler, Jessica Virtus Troy Lawrence Young, - First Citizens Securities Corp 8415, 0613 B4

1 100746 11/1/2013 Salerno, RJ Virtus John O'Neil, - Merrill Lynch VIR003, 1
1 100746 11/1/2013 Salerno, RJ Virtus John O'Neil, - Merrill Lynch VIR008, 0112
1 100746 11/1/2013 Salerno, RJ Virtus John O'Neil, - Merrill Lynch VIR021, 1

Basically a client pays a price per order, and a price per additional item in the order, so I will sum these up at the bottom of the spreadsheet.

Any help in the right direction would be appreciated. The new orders always have a blank row above it so the formula can basically say if cell in column "C" is blank do this until "C" is blank again.

Thanks
Ryan.

in A2: =IF(and(Countif($C$1:C1,"="&C2)=0,not(C2="")),1,"")
in B2: = IF(and(Countif($C$1:C1,"="&C2)>0,not(C2="")),1,"")
and copy down

Hi Ryan,
Assuming that de column Order is col. A and the order number is in col. C. Put in col A the formula =IF(C1="";1;"") where C1 is on the row above the formula, thus in this example the formula sits in A2. This will put a 1 in front of each new order.
Put in col. B the formula =IF(C2<>"";1;"") on the same line as the order number (thus in this example in cell B2). Then pull those down as far as needed.

best regards,
Carl