I agree with Peter - this might take an hour or so, but it'd take that much time (or much longer) to build a VBA utility to do this.
That said, you can certainly apply permissions to Groups, and you don't need to "assign" a user to a particular object. Security constants are hard to find; the only definitive source I've found is in the Microsoft Jet Database Engine Programmer's Guide (Second Edition), from Microsoft Press. This is out of print, but there are plenty of copies available on the big book websites.
The constants you might need for "open/run" for queries/tables would be:
dbSecReadDef
dbSecRetrieveData
dbSecDeleteData
dbSecReplaceData
dbSecInsertData
For forms and Reports:
acSecFrmRptExecute
acSecFrmRptReadDef
acSecFrmRptWriteDef
For databases and other:
dbSecDBOpen
dbSecReadSec
dbSecWriteSec
These all came from the above referenced book.