Does that mean that my AMD Athlon XP 2800+ won't be able to run it due to not having SSE2?

Well, it probably means that they just haven't tested extensively such CPUs? - they are saying that about graphics cards with 256MB.

I can run this hardware test with no problem even that I have one core CPU and 256MB of memory on graphics card.

I do not think you will get any other answer from forum users before release of the game.

Was just hoping that a dev would see this forum, guess not.

You'll have more luck over at grimrock.net

I think the devs are on the forums there. :)

Game is running fine on my single core Pentium 4C (at least first levels).

Oh, yeah.
Meant to post about my results.

The game runs perfectly on my AMD Athlon XP 2800+, so glad I took the plunge.