It would probably be easiest to do (from an understanding aspect at least), but you could also. . .
Run your normal query. There will need to be some form of sorting/ordering built in (for the next part). Be sure to limit your Query to (n + 1) Records using TOP (n + 1).
Then you Query the results of your first Query using the opposite sorting/ordering using TOP 1.
Example:
You have a Form called frmMyForm with a Text Box called NthRecord.
qryQuery1
Code:
SELECT TOP ([Forms]![frmMyForm]![NthRecord] + 1) * FROM MyTable WHERE [Field1]='foo' AND [Field2]='bar' ORDER BY [DateField] ASC
qryQuery2
Code:
SELECT TOP 1 * FROM qryQuery1 ORDER BY [DateField] DESC