Yes, if it is a Text field, Access would not be dropping the leading zero. It is getting dropped before then.
In order to compare the two files, you will need to add the missing leading zero in. There are a few ways of doing that:
1. Updating the Access table after import (using an Update Query)
2. Adding the leading zero in via a calculated field in a Query, and link this query to your other table
If doing option 1, create a query that select all ID fields where the length is 4. Then update it like this (in the Update To row):
If doing option 2, use a calculated field like this:
Code:
RealID: IIf(Len([IDField])=4,"0","") & [IDField]