Multiprocessing: Oracle 7 & Solaris 2.3. How much?

I'm investigating using Oracle 7 on a multiprocessor Sun platform (SS20 or SS1000) running Solaris 2.3.

The system will have to support multiple concurrent users, so a multiprocessor system is obviously the way to go. Unfortunately, the SQL each user executes is rather complex, and it would be nice to see a multiprocessor system helping out there aswell...

How successful is Oracle at dividing query/update load over the processors?

Does it rely on spawning 'server' processes for a transaction that Solaris can run on separate processors, or does it go 'deeper' and break queries up into atoms that can be run as threads on separate processors.

How much do we get for 'free', and how much parallel processing / multithreading do we have to code into our applications?

We have received conflicting information from Sun & Oracle sources, so it would be great if someone who had actually used a configuration like this could shed some light on the subject.

Thanks,

-- 
Richard Williams                         Email: rdw_at_reflex.co.uk
Reflex Manufacturing Systems               Tel: (0293) 560111