convert int to numeric (formatted) string

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vs2005 c#

hi:
need to convert a simple int to a format nnnn. if I have int 1 I want the
result to be padded with 0s as 0001 on a string

I have int 1 and I want "0001"

any help. Thanks

so far these dont work
field.ToString( "nnnn") or field.ToString( "####")