Have a budget of almost 100,000 Yen (about £400?) Primarily building for Spore/Starcraft 2/Stalker/Guild Wars 2 and to run the PC version of Oblivion (so many great mods you cant play on the 360..)

Already picked:
ABIT KN9S, nForce 550
TwinMOS DDR2 PC4200 1024MB Dual Pack CL4   
AMD Athlon 64 X2 4600+ 2.4GHz Socket AM2 1MB   
Gainward GeForce 8500GT 256MB DDR2, PCI-Express, DVI/Tv-Out

Case (with PSU included)/SATA hard disk recommendations anyone?

Im liking the Seagate drives i bought.  5 year warranty is a wonderful thing.  
Cheap is reaonsable, and i assume they are cheaper there?

Only slighty cheaper:
http://www.dospara.co.jp/top/
http://www.primepc.jp/goods_pc_parts/goods_pc_parts.php?dr=10&sc=1&iv=y&stk=0&brcode=13&sbrcode=172
http://www.komplett.co.uk/k/ki.aspx?sku=320708

omg when was starcraft 2 announced ? I need to book a year off work. I lived on starcraft since 1997.

Quote from: Samomg when was starcraft 2 announced ? I need to book a year off work. I lived on starcraft since 1997.

Couple of weeks back.

http://eu.starcraft2.com/

awesome, sc is easily the best game ever.

http://www.youtube.com/watch?v=-x0tS506hdk

Oblivion with an 8500GT will probably be just OK @ low res.
Turning all the goodies to there lowest settings may give you playable frame
rates.
As for a case it is the PSU that is probably the most important so for a budget case with a descent make/power PSU.
http://www.tekheads.co.uk/s/product?product=605580

Quote from: Samawesome, sc is easily the best game ever.

I remember you harping on about Starcraft!!!  :-)

lol I still played it up to 2006.

starcraft... what a classic

in regard to your GFX card...

http://www.st-athersystems.com/index.php?act=viewProd&productId=35

seems a really low price... or you could spend a bit more and get a card that meets your needs, like a 7600GS (about 70 at a good price)