SELECT * from table1, table2 where table1.field1 > 20031126 and table1.field2 in (select field3 from table2 where field4=5)

is this possible ???

1) I am not sure whether mySQL supports subquerys.
2) I don't get what you are trying to do? Should there be something between 20031126 and table1.field2

Even if it does allow sub-queries, your query will produce a cartesian join. You have not joined table1 and table2 in your main query. You might want to rewrite it as.

select table1.*.table2.*
from table1,table2
where table2.field4 = 4
and table1.field2 = table2.field3;