Spring RTS Engine

Is my system enough to run Spring?
I have

1gb DDR2
Sempron 3400+ 1.8ghz
Radeon X800XL(Opensource drivers)

When I start ZK, it starts out fine, but as it progresses it slows down to 1-2 FPS and finally freezes. I use LMDE 64-bit, so I've tried running swapoff -a to free up the swap when it started to get filled, but it didn't work. Is there anything I can do on the software side, or is it hopeless?

GFX is the problem, most likely, in this case. ATI makes horrible GFX drivers for OpenGL, and even worse on Linux. the open source ones are sometimes a bit more stable, but in return perform worse.. looks like in the case of your card, they are not stable even.
In other words... try with the closed source drivers, and try to get NV next time, if you like gaming on linux.

But I read somewhere that my card is the ATI card with best open-source Linux support.

well I've heard cpu is often the bottleneck aswell and in your case it is quitte horrifying to play spring on.

Even with my (laptop) i7 its not always smooth enough...

You can expect to not have an enjoyable gameplay experience in anything over 3v3. The lack of RAM and poor budget CPU is the main reason why the game will run slow under any OS and the lack of good ATI drivers for Linux is the reason why you will have crashes in Linux 64-bit.

There are no hardware & software requirements on the homepage anywhere near the download section.

I dont habe a good overview of the player base and its hardware, but I'd write there something like this:

* CPU 2 GHz or more
* RAM: 2 GB or more
* GFX: NV???/ATI??? or higher, all other vendors are useless

* WinXP SP3, Vista, Win7 32 & 64 bit(?)
* Linux see Linux-guide

@linux-guide: you must use closed source drivers or your FPS will be useless

For some reason, Spring is playable now.
I'm not sure if it was the upgrade to the new 2.6.38 kernel, or getting noatime to work, but I can play with decent FPS now .