When importing a .CSV into numbers I lose the 0 at the beginning of my zip codes, how do I get them back?

you can format the cell with a custom for mat for zip codes like:

select the cells to format, then open the cells inspector. Select the "Custom..." entry in the Cell Format menu

Set up the formatter as shown:

save the custom format using a name

What version of Numbers do you have? I was demo'ing from Numbers '09 (version 2.2)

you can add a new coumn following the zip code and enter the foloowing formula, then fill down as needed:

actual ZIP is in column C, new column "Aux ZIP" in column D:

D2=IF(LEN(C2)<5, "0", "")&C2

select D2 and fill down

now copy column D and paste values into column C (then remove column D). To paste values use the menu item "Edit > Paste Values"

Happy Wedding!