I got this game and was messing around for awhile and noticed it seemed to be running way to fast, garbled audio, and some weird game play glitches. Currently the fix is hit Alt+Enter once you load up Shattered steel, then hit Ctrl+F12 to lower the CPU cycles. You can see the percentage at the top of the dosbox window. Around 45-50% and the game runs perfectly for me. Hope this helps some people out. Oh for reference I'm using an Intel Core2Duo Clocked at 3.0Ghz.
Oh forgot to mention once you get the speed correct, hit Alt+Enter to go back to full screen.

Thanks for the tip!

sadly, this doesn't work for me. I set it down to 6% and used only 1 CPU, but still get this weird "speed boost" while moving. Every few seconds the game runs overall at high speed.

Intel Quad Core 2,66GHz
8 GB Ram
Vista 64

Does anyone got another idea how to "smooth" the gameplay?

This is quite the late response. What you can try doing is setting the core type in dosboxShatteredSteel.conf from 'auto' to either 'normal' or 'dynamic'. For newer CPUs go with 'normal' since it can handle the more instruction based emulation.