The number of times I've beenstung by "futureproofing" my PC is more that I care to remember. Every time it is such a good idea, then I see that a newer, better, smaller one is there when I upgrade (e.g. My SLI compatible motherboard - cheaper and better to get a new GPU than a second old one).

A PC that lasts 3 is doing well.
And let's not forget Windows Vista is coming out with all new requirements for everything. This type of things will probably repeat every now and again, as happens with standard features in graphics cards. Older ones just don't have them.

IMO get a nice case. Get DVD/CD drives you like, as well as speakers and a monitor, and accept that the CPU, motherboard and graphics card all need to be replaced together.

My brother is going through this: keep the old memory - well, that's a speed bottleneck.
Keep the motherboard: old bus, doesn't have the mdern CPU compatibility.
GPU: too slow
CPU too slow.

But then I like making my PC as then I know what is in there, and have an idea how to fix it.