How to show zero as a first number

I am a beginner at Excel and would like to know how export numbers into another spreadsheet that begin with zero, at the moment it deletes them, I would like them to remain as they are bar codes, I have to import a thousand of lines at a time, some of which begin with a zero and some do not.

It seems that when I copy and paste, the numbers paste in OK but not the format, so the numbers that begin with a zero effectively lose that zero and the numbers that begin with any other number paste accross unchanged.

I can Format cells, then in custom change type to "0"# but this simply adds a zero to every number in column, if I could import the correct number into Excel to start with it should work. I realise this is no doubt quite straightforward but I just can't work it out, help!

Many thanks

Paul Smith