You can never have too much RAM. 8 gigs is
preferable. When you do get your copy of Windows 7 make sure
it is a 64-bit copy. The 32-bit version won't be able to use
all your RAM otherwise.
Power supplies are more important than folks realize. One
brand I know that I like is PC Power and Cooling. I'm not
sure about the availability of their PSUs in Singapore.
Skip the SSD. Get a standard hard drive with 7,200 or
10,000 RPM spindle speed. I believe both Seagate and Western
Digital make 10,000 RPM drives. I think Western Digital calls
it the "Raptor" line.
Get a tower case that can accomodate several fans. If
you're not overclocking your CPU you can probably go with whatever
stock heatsink comes with the chip.
For games you do *not* want to use any graphics chip that may be
on the motherboard. You'll need a dedicated video card.
The choices then are a video card that is either Nvidia or ATI.
Don't get the absolutely latest and greatest video card.
They cost a fortune and in 6 months that card will be overtaken by
a new model. Get the video card one step below the latest and
greatest. You can always swap in a new video card later.
For the motherboard any of the major manufacturers are
fine. Almost all of them are made by Tawainese
companies. Intel has its own line of motherboards.
A DVD writing drive is pretty common these days and shouldn't
cost you a fortune. Skip on a Blu Ray writing drive.
The media cost too much and you will rarely need that much
storage. External hard drives are a better choice for
portable storage.