I have a spreadsheet with three columns, each column has approximately 1200
cells
with part numbers entered into them. I would like to find duplicate numbers
across the columns and have them highlighted. Is this possible?

This is an application for conditional formatting. My understanding is that
you have a database that is 3 columns by 1200 rows and for any given row,
you'd like to highlight any duplicates in that row. Assuming that your first
row of data is in A1..C1,

1. Select cell A1 and click Format - Conditional Formatting.
2. Choose "Cell Value Is" "Equal To" and in the third box, type =B1
3. Click Format, choose a desired highlight color, and click OK.
4. Click the Add button and do the same thing except type =C1, then click
OK.
5. Repeat steps 1-4 for cells B1 and C1 except in B1 use =A1 and =C1 and for
C1 use =A1 and =B1.
6. Now highlight cells A1..C1, click Edit-Copy, then highlight cells
B2..C1200 and click Edit - PasteSpecial - Formats, and click OK

This will highlight any cell that has a duplicate value on the same row. If
I have misunderstood your objective, then please clarify.

"He cries for help" wrote:

I have a spreadsheet with three columns, each column has approximately 1200
cells
with part numbers entered into them. I would like to find duplicate numbers
across the columns and have them highlighted. Is this possible?