help_sql_please

Could someone please help me with the following: When I write a query with the following format I get the error (ORA-00979) message "not a GROUP BY expression" at the first decode statement in the select clause.
When I add the decode selections to my group by clause, Oracle dosen't like this either (ORA-00998) "Must name this expression with a column alias.
Is there a way out that will allow me to use decode statements rather than multiple virtual table joins? (My actual query uses 24 decode statement and the corresponding query with virtual tables is unwieldy)

Thanks in advance!
Doug Hersh -- enquad_at_world.std.com

select

	T1.VALUE,
	T2.VALUE,
	Decode(arguments) alias_1,
	Decode(arguments) alias_2
from
	TABLE1 T1,
	TABLE2 T2
where
	conditions
	and joins
group by
	T1.VALUE,
	T2.VALUE