I just got an old Voodoo3, and it's a nice graphics adapter, but the rest of the machine (K6-2, 400 Mhz) cannot decode Mpeg-2 fluently. Then, I read that the Voodoo3 itself should be able to decode up to 30 frames fluently without problems.
However, it doesn't work with me, even when using the old PowerDVD 4 (heard that this one would support the Voodoo3, 16MB).
I'm using the AmigaMerlin-Drivers under WinME.
DirectX 9.0c is installed.
Hardware-Acceleration in PowerDVD is activated.
I cannot use WinXP due to an old ISA-SoundCard (no drivers).
Should I use other drivers or another MPEG-Decoder?
Because there is no speed difference between Hardware-Acceleration enabled or disabled, and it just doesn't work fluently...

...that... and overclock that K6-2 to at least 500Mhz, if not 550Mhz  with jumpers; and then - it should go fluently. I had a system like that some 8-9 years ago You could get a new heatsink that should have no problems cooling that CPU @ 550Mhz.

Place the jumpers to 5.5 x 100Mhz... Good luck  8)

I have P3 800MHz and Voodoo3 3000 16mb

and movies run well with VLC player <-try that its very good program. It is able to show all video formats

First of all, I have to express my thanks, I would not have thought that so many people are still interested in 3DFX-Cards.
I have already tried the original driver, it didn't help, though I have not tried WinDVD (yet). VLC is much slower, and somehow, the OpenGL-Output doesn't work there (don't ask me why!).
The interesting thing is, when I overclocked at 450 MHz (didn't want to risk more), it did NOT become more fluently - however, when I disabled the sound, it ran mostly smoothly. CPU-Load then was something about 80% - 90%.
Maybe, it's a sound-acceleration-problem, too, because in VLC, the sound only is garbage (it seems to play the audio of normal MP3's two times at the same time!) and in PowerDVD, I can neither mute nor adjust the volume (it always shows 0%, though the Windows mixer works normally). I use an old ISA-Card from Miro (Miro Sound FM 10), but maybe I'll try to change that because that seems to be the real problem.
I already disabled all postprocessing in PowerDVD (and VLC), though deinterlacing stays active all the time.
The fact that the speed is not much different when using the AC3-Stream for sound makes me think that there might simply be a VERY slow sound driver.
With MP3s, the CPU-Load is somewhere around 50% with the Windows Media Player, and at about 25% with VLC (but just garbage). PowerDVD uses about 25%, too, but plays things correctly.
The problem with the Media Player from Windows is that it finally uses PowerDVD's routines for decoding (there is no built-in MPEG2-Decoder) and is not that optimized.
Still, I do not understand why VLC is so slow.
I have asked somebody on #voodooalert (QuakeNet), and he now tries to compile a GLIDE-plugin for VLC (which was originally written for Linux) for Windows. Knoppix doesn't include VLC, so I could not check whether it works, and I did not find the time (not yet) to install Linux (and then, I would not have any sound drivers).
So, I'm still trying to find the problem, though it might really be sound-related. Oh, and I have enough memory - 256 MB
For now, I can just thank all of you, I didn't expect that many people to reply

That's the one I might choose, it's somewhere in this far too big, though too small house in an old machine. With a full WaveTable-Memory
I also have some PCI and even an AGP-Slot in this machine, but no newer Soundcard, but the AWE (32? 64? can't remember which one it was) should be ok. Will try in the next days.

Sorry it took me so long, but finally I made it: I used a SoundBlaster AWE 32 with the normal Windows-Drivers, and though CPU-Load is at 100% in PowerDVD, it seems to run smooth. At least, the Audio-Crackling has gone that was there before. In VLC, it's still not working (far too slow), but the sound works now.
However, it's very interesting that I can only hear audio through PowerDVD if I put the volume to exactly 100% - otherwise, there's absolute silence.
Still, I'm not sure whether it's running completely fluently, because I have not found any FPS-Option in PowerDVD yet - at least, it should work now, though I can't be absolutely sure about High-Motion scenes.
And the CPU-Load for audio-only dropped to about 5-10% when listening to an MP3 - that's perfect!
The other problem is, that the AWE 32 with full wavetable is quite big - I'm currently running the machine without case, and I thought about building one, and now it would have to be nearly double as long...

@Elfuego: Thanks for the idea, it solved the problem. However, I think the Terratec-Soundcards are also quite nice - at least the surround ones But concerning stereo and ISA, SoundBlaster AWE 32/64 really is the best. (Somewhere, there should also be an AWE 64 here...).

@Combatman: Thanks, the problem might help to resolve this 100% CPU-Load - but maybe, this is also FPU-related, because the Pentium II is much more efficient.