If you add an Autonumber field, then each record should have an identifier from 1 to 1,000,000.
Then, you can create a query and place criteria on your Autonumber field to just pull out the subset you want. As matter as fact, if you make this a parameter query, it will prompt you for the numbers at run-time, i.e. place this as the criteria under the Autonumber field in your query:
Code:
Between [enter lower limit] and [enter upper limit]
Then when you run it, if you enter 1 for the first prompt and 250000 for the second prompt, it will return the first 250000 records.