use DMax()+1 to generate the autonumber.
since it resets every year, you also need a year field (number) to your table.
dmax function is not available in macro so you need to build a function to generate.
you also need a form for your table so you can call the function.
add code to your form's BeforeInsert() event:
private sub form_beforeinsert(cancel as integer)
me.autonumberField = nz( dmax("autonumberField", "yourTableName", "yearField=" & Year(date())), 0) + 1