[twillight]

I'm no professional with hardware, but lemme give some inside how I think you should go anyway.

10 years might be alittle more then you can have on a trustable bases, but let's try the best.

Two HDD is way better solution the two partitions. 500 GB HDDs are very cheap, even 1TB disks are perfect quality nowdays. Considering the machine can include 8 HDD, there is no reason to try sparing here.

Operation-system: get your prime a Win7. Home Premium is fine. XP is "left behind" currently, like still trying to use Win98 today.

The particles come from two major company (I think ATI vs. Gefore-Nvidia, but don't hurt me for this), I suggest avoid mixing the two. Seems to be personal preference above that (but with ATI it seemed like trying Macintosh instead of PC for me).

From RAM 4 GB can be satisfying already, even without graphic card. Above 8GB you won't be able to use what you actually have (according to the shopkeepers I asked), and even on a superb construction there is no reason to have more then 16GB RAM (especially as it'll start literally eat energy).

All the periferies (DVD-drive, mouse etc.) seem to not evolve too much, so even cheap basic ones will serve proper. Heck, they even might last longer then more expensive ones.

The CPU seems most important choice.

From graphic cards I say buy the one after the first big rise in price. Those will last for some coming years while remaining stable and don't overheating or such. Above these the prive/value ratio exponentially drops.