Create a lookup table with two fields, something like:
Then, enter the hierarchy you want them to appear in your drop-down (i.e. High=1, Moderate=2, Low=3).
Then, go to the table that has the fields that you are setting. Click on the field in design view in the table, go to the Lookup tab, and enter the following:
Display Control: Combo Box
Row Source Type: Table/Query
Row Source: build a query based on your lookup table where you display "MyName" but sort by "MyOrder". The SQL of that code would look something like:
and enter the table name of your lookup table in theCode:SELECT LookupTable.MyName FROM LookupTable ORDER BY LookupTable.MyOrder;