Hi,
If for instance your first 5 numerical characters were always 45672 then in the Input Mask field in your table for that particular field you can enter either of the following:
"45672"9999999
With the "45672" enclosed in double quotes, when ever a new record is created these five characters will always appear in the field, the 9999999 characters are place holders and can be either a numerical character or a space.
If you don't like the 9 place holder you can use the # place holder which does the same job.
Again whenever you create a new record these five characters will appear first, you just simply enter the required characters where the place holders are.
Hope this is of assistance.
John