Hi,
rnahi is right. If you want to see how many rows are effected and how the joins are done execute a

explain SELECT AM.AM_A, AM.AM_M FROM AM,AR,SA,MR,SM,SR WHERE AM.AM_A !
+=
+ SA.SA_A && AM.AM_A != AR.AR_A && AM.AM_M != MR.MR_M && AM.AM_M != SM
+.SM_M;
[download]

in your command line mysql client. Any query that has table joins like 'ALL' are bad news. These are the cartesian product joins rnahi talks about.
for more information about this check for instance http://dev.mysql.com/doc/refman/4.1/en/query-speed.html
if the explain query gives you a reasonable amount of rows and joins and you still have a problem with DBI, return to the monastry!