Hello,
I have;

Intel Q9450
2GB Cosair RAM (Twin2X2048-6400C4)
Asus Maximus Formula
160GB HDD Hitachi 7200RPM
8800 GTS EVGA
Some really low end case

My two questions are;

1. Is the Antec twelve hundred better then the nine hundred or just bigger? (Air flow wise). Will I have any trouble with the nine hundred being to small for those parts?

2. Is the RAM I have now worth upgrading (Same RAM just adding 2GB) to 4GB

1. While the 900 may look small, but the ventilation is pretty good. It'll fit 2 GTX 200's.

2. Yes, get DDR2 ASAP or their prices will go up once DDR3 goes mainstream.

Ok cheers, I got an extra 2 sticks of RAM (4X1GB now).

The RAM I have bought is CL4 and I'm sure when you put them in the computer, it boots up with them at CL5. Is it worth pushing them down to CL4 in the BIOS or won't it really make a difference?
I've heard there are problems overclocking with 4 sticks of RAM in the motherboard. Is this true and why?

When I upgrade to 8GB RAM sometime next year is it worth getting 2X4GB?

I'll get the case next month. I'll get the Antec twelve hundred because of the option to control the fans more easy.

You most def. need to bump up vdimm to 2.1v-ish, depending on the ram specs for the CL4 to work. You can try stock vdimm, but if it won't post, you'll have to try each stick of ram in each slot. CL4 won't be noticeable to your naked eyes at all. All the sticks must be CL4-rated or they won't do it at all.

I o/c my e8400 to 4ghz prime stable with 4 sticks of ram. It's a matter of config. Both hardware & software (bios).

32-bit os uses up to 3.5gb of ram. 64-bit os uses 4gigs+. The amount of ram to get depends on the os.