1) 2) 3) Wait a while for the new Intel Conroe CPUs. They might use a whole new socket (I think). All and all, I say wait another 3-6 months instead of building a PC now that can't be upgraded 18 months down the line. I'm not sure, but I think that when AMD moves to AM2, that they are going to a new socket as well. And even if they didn't, you would have to get a new Mobo anyway that supports DDR2. If you decide to build now, the Opteron 165 is a very good choice. If overclocked, it will be as fast as anything else out there at the moment. Keep in mind that even if, lets say, the AMD FX60 which is pretty much the fastest CPU out there today, can't be upgraded in the future, it will be at least 5 years before it reaches the bottom of the performance league! At which time it would be time for an upgrade anyway! So getting a good CPU now will always be a good investment!
4) Go for the 7600 now, and wait for the DX10 cards.
5) 2 x 1GB should be fine for now, should be fine for at least 6 months. Not sure, but one would assume Vista will support that much memory.
6) For you Mobo to access the DDR500 at its intended speed, you would have to OC your CPU. AMD CPUs run with a 200MHz "FSB", meaning at 400MHz efective with DDR memory. Even if you have DDR500, if your CPU is running at stock speeds, it will effectively underclock your DDR500 to DDR400. Simply up your "FSB" to 250, and your memory will run at DDR500 speeds.
7) I think for DDR500, should be something like 3-4-4-8 for the best. DDR400, try for 2-3-3-5, or 2-2-2-5 for the ultimate! Anybody can correct me, but timings don't really make a **** of a lot of difference at stock speeds. But the lower the stock timings, the more (I assume) they can be OCed.
8) DDR2 runs at faster speeds than DDR, but have worse timings and are more expensive. The advantages Intel gain by using DDR2 are negated by the fact that AMD 64 CPU have the memory controller on the CPU, thus enabling quicker communication between the CPU and RAM. Go for AMD instead of Intel if building now. If your going to wait, go for the Intel Conroe chips (see point 1).
9) Cases are your choice, depends on your preferences. Dont buy a case with an included PSU. As for PSUs, Antec/Fortron/OCZ
10) Cache and RPM play a big part. Obviously, the quicker the drive revolves, the faster, and more expensive it will be. SATA3GB is the fastest interface at the moment, but you as an user will rarely see or feel the difference in speeds. No matter what people say, I don't think the price of a WD Raptor 10k drive justifies the 5 seconds less it takes to load a game or program. The major differences in speeds between cache sizes and RPM and interfaces can only truly be noticed in synthetic benchmarks. If you are on a budget, buy what fits your pocket. Look at things like $/GB when deciding on drives.
2ms is overkill, you won't see ghosting on any new LCD below 8ms response times. I could be wrong, but Windows Vista uses something like DHCP which might mean your monitor might not work with Vista. The new 7900 series of cards already support that. Please don't take this as a fact, wait for what other people say. I'm pretty sure LCDs use DVI, which all new graphics cards have anyway.
Hope it helps a bit! Cheers