Well, your computer is about on par with Xbox360...
You see, the Xbox 360 would blow your computer away if it had 1GB of memory, instead of 512MB shared memory...
Round one:
A64 3500+ is pretty good, but Xbox 360's three-core CPU (each core running at 3.2GHz) is definately faster, hands down.
A64 3500+ beats crap out of one of these cores (it almost performs at the level of two of these cores together), however, it cannot beat three-cores, especially if the program has properly been coded for multi-threading.
So Xbox 360 CPU > A64 3500+
Round two:
7800GTX vs XENOS
7800GTX has 24 pp and 8 vp, XENOS on the other hand has 48 parallel floating-point dynamically-scheduled shader pipelines - so called Unified shader architecture.
The unified architecture aint as nearly as strong as dedicated pipelines - 48 UA pipelines operating as pp will equal 32 or less dedicated/real pp for example, however, keep in mind that a huge advantage is that you can switch on the fly between pp and vp on UA pipelines, giving you a tremendous perfomance boost. You can instruct how many UA pipelines should act as pp, and how many as vp, a great advantage for sure, not to mention 10MB of embedded RAM - which offers practicaly free AF/AA and gives a huge boost to fillrate...
I won't throw around any numbers, because they tend to be very uncertain and a pure product of PR.
But in short, just because of these two things above XENOS is better than the 7800GTX. Thats why Nvidia admitted UA is the way to go, and will base it's future products on it.
So, XENOS > 7800GTX.
Round three:
Memory, well here's where Xbox 360 falls really, really short.
The have gone for the unified memory architecture, but that aint so great as UA for GPU pipelines. It has a total of 512MB which are shared between the system and GPU, the good thing is you can have more than 256MB for textures, the bad thing is that you have a total of 512MB to begin with (just remember how FEAR has a distinct improvement when going from 1GB to 2GB, and Xbox 360 has only 512MB!), and the second, you have to share that memory between the CPU and GPU effectively.
Your 1GB system memory + 256MB dedicated GPU memory on 7800GTX sure beats the hell out of the Xbox 360 memory subsystem, it may not be faster, but the amount it self is able to give a clear advantage with demanding games...
So your memory subsystem in general > Xbox 360's
The third part plays a really major role - even when developers start optimizing for three cores effectively, they are still going to miss the RAM, and a LOT of it. - If they assign 256MB to GPU, that only leaves 256MB for the rest of the system, and 256MB aint enough for next-gen games, even if you dont have windows running in the background...
So all in all, your computer should be in most cases on par with Xbox 360 in next-gen games, cause they wont have enough memory to show Xbox 360's potential, and it's truly a great system - the UA for the pipelines is something I have been looking forward for years...
However, the UA applied on the memory subsystem is also a great idea, but you have to make sure there's enough RAM for both CPU and GPU in the case they are being loaded with lots of data, 768MB perhaps would have been enough, 1GB really great, however, 512MB is one of the reasons Xbox 360 games wont look as they are supposed to.
I know it had to be done to cut costs, but still...
However, your system is still great, no doubt about it, and the fact you can ugrade to a second 7800GTX will give you a nice performance boost
, then you will definately outperform the Xbox 360.
