I don't think its a Windows Vista issue as I run that OS and Kingpin runs fine.
I have Windows Vista Home Premium 32 bit version. Duel core CPU with GForce 8800 GTS graphics card.
The ppl who are having problems who are using Vists. Are you using 32 or 64 bit version? Maybe its caused by Vista 64 bit if thats the case.
I assume everyone has patched the game to v1.21? If not you can get it as part of the KP starter pack from here - http://downloads.kingpinforever.com/kp_starter_pack.zip
I'm not running KP in any compatability mode or even as an administrator but I suggest ppl who are having probs try doing that. You could even try disabling visual themes in the Compatability tab.
I know KP has issues running with laptops with onboard graphics cards but I think that is only when trying to run the Monkey mod cheat protection client.
It may also be something to do with your monitor refresh rate.
I have Windows XP 32bit, so it may not be an OS specific problem as you indicated.
And the game comes up-to-date with the 1.21 patch already installed.
Disabling visual themes had no effects.. neither changing the refresh rate, but with a bit more investigation in that direction I managed to solve the problem. Kingpin doesn't like setups using two monitors in Dualview mode. As soon as I set it to use just my main monitor, all the stuttering went away. Thanks a lot for your input!
odd, because when I get the stuttering it's on my laptop..