looks like a solid build, case might be a bit of a tight fit in the end (handling things, etc), but it should all fit in there just fine. I'm just more accustomed to larger cases like My Thermaltake Armor case, or the Coolermaster Stackers.
yeah for the time being, unless your running XP Pro 64-bit, you won't be able to use all of your systems RAM, you'll be stuck with about 3GB max to use till you upgrade to Windows 7 64-bit (if you do)
32-bit can only address up to 4GB (4096MB), subtracting the GPU's memory, HDD cache, and CPU Cache, just to get a rough estimate would give you your available RAM for windows, but even still 3GB is plenty for now.
my i7 build will only be running 3GB right now too, till I upgrade to another 3-6GB more.
with my setup though, I'm hurting more than your would be, running XP 32-bit right now as main OS, and Win7 RC 64-bit for secondary. figuring 32-bits 4GB max, it'll leave me with less than 2GB for the system, I'm running 2x Radeon 4870's 1GB each, and 4 drives as well, 1x 32MB Cache, and 3x 16MB cache drives, and the same CPU as you (i7 920), not factoring in optical drive cache memory, etc.
luckily I'll be also using Win7 RC 64-bit for the time being, which will help me out considerably with the dual cards, and some of my 3D apps to use all the system RAM.