What PSU with this case

After my 8 year old nephew busting the front USB ports on my M-Atx case & deciding its taking up too much space on my desk I'm thinking about buying a new case (probably this one)

http://www.scan.co.uk/Products/Produ...oductID=378733

I'm assuming it will take a Standard ATX psu - probably going to go for a Seasonic again as an S12 430 is doing the job nicely in my gaming rig - but would a lower wattage model do the job? (I want a quiet PSU too as the case will sit right next to me on the desk)

Specs
S939 4600+ x2
Asus A8N VM CSM-MBP
1 stick of 1gig Kingston PC3200 ram
Samsung SP2004C HD
Nividia 128MB 6600 GC
LG dvd writer

Reccomendations please