A couple of problems I have with AF, running on a 2gb dual-core Vista rig, is that it runs WAY too fast to make it enjoyable. There doesn't appear to be a frame-rate limiter (come on guys; 1.19 patch crew should have realized we all have faster rigs than in 2001) so the character runs around crazy fast.
Also, I cannot get the stealth mode key to work, regardless of where I map it to. That's a deal breaker.
I'm dissapointed it was released to modern systems with these problems.

Games running far too fast usually means a timing issue across multiple cores. This frequently occurs if you have power saving on. The CPU timers are not guaranteed to be in sync (coders need to use the OS API and not directly interrogate the CPU) and thus speed variations in the CPU become massive timing problems in games. I've seen this first hand with Deus Ex. Usual culprits:
a) Control panel -> Power options. Make it desktop or maximum performance.
b) Start the game, then alt-tab out and start Task Manager. Right click on the application and press Go To Process. Right click on the process and choose Set Affinity. Make sure only one CPU is selected.
On the rare occasion I have seen problems with games and graphics drivers, so you may want to
c) Ensure the vertical refresh rate is locked to enable (use NVIDIA/ATi control panel)
I'm pretty sure every game since about 1993 has used a lock to a timer rather than just running a loop as fast as possible, back when computers were a few MHz.

I just switched to single core operation, but that introduced some crazy lag, making it worse.
The solution (for me) was to install it on my old P3 800 XP rig, where it runs just fine. If any of you have old towers gathering dust, check out a KVM Switch. It allows 2 (or more) computers using the same Keyboard, Video (monitor) and Mouse. I just double click on ScrLK and it switches between my old XP rig and my new Vista rig.

Game worked fine on my rig... it's not that great but it's also not that old, I'm running a Geforce 8600gtx with 2 gigs ram athlon 3300 ish (forget exact number, somewhere low 3000s). It's normal speed, but then again a single core cpu

Thats just weird. I have an intel dual core vista rig and haven't seen any speed problems. I got a host of other ones though thats really taking away from the immersion this game is famous for.

The character should walk quite slow, if you played it when it first came out. Not the running speed it does now. Playing it on an old P3 800 fixed this. Does your character walk slowly (tthink Fallout 3) or cruise about merrily (half life 2) ?
Edit: removed the part where I was a bit of a prick.

When I first ran the game my character was zooming all over the place (everyone else moved at their normal speed). Possibly this had something to do with my adjusting the resolution upwards and to widescreen, because when I did it made the in-game interface tiny.
When I quit out of the game and ran it a second time, the Interface graphics were back to their correct-proportional-to-the-screen size (though they're now very pixelated), and my character had seemingly gone cold turkey on the caffeine.

IF you have an AMD dual core install the amd dual core optimizer. Same thing happened to me with painkiller and it got solved with the optimizer.

hm, well i just started playing Arx for real. My character does run around like a rabbit on speed and everyone else is normal. I'm also not sure whether sneaking is really doing anything, but since I'm running so far the difference might be difficult to spot... I'm using a single-core Athlon, any idea why my game would be making my guy run around so fast? Resolution issue as someone mentioned above?

My guy shoots up and down the hall like he's on a nasty combination of meth and crack. I have a fraps video of it, just nowhere to put it. (Too lazy to make a YouTube account... and it would be pixellated all to hell anyway.)

I figure I'll necro this, because I'm having the same problem...it makes the game nigh unplayable...I hit W once and the guy zooms across the room like no one's business.

Try googling for AMDs Optimizer tool if you are using an AMD processor....

I've got an Intel Core 2 Duo processor

64bit or 32bit Windows?? And which version?

Windows XP Pro 32bit, Service Pack 2