seperate a string

Hello-

I have a field that is a 'string' which can have 1 value in it, 4 characters, or it can have numerous values in it, up to 240 characters.  The string could look like:

1234

or

123456789012 ....up to 240 characters

It will always be either 4 or in increments of 4.  There is nothing separating the data. I would like it to show every 4 characters + a 'space' + the next 4 characters + 'space', etc.

1234

or

1234 5678 9012

Any help?

thanks!