I got this slow motion experience too. At first, it looks okay. the graphics also looks good though, but then after 3-4 seconds, it became slow motion. I found out that the slow motion effect comes out when there are more players on the screen (usually near the penalty area). FeDe, I already did everything that you suggests but the problem still persists. (V-Sync Off, basic acceleration for sound in dxdiag). Btw, how to run the game in Windowed Mode? When i set that option on, it appears that the game run in Full screen as well. I'm really disappointed because Konami set the benchmark too high for pc requirements. It's a shame because I can play Fifa 2004 Demo on 1024x768x32 without any problem (Btw Fifa's graphics looks great too!) Personally, I love this PES game, I even play Winning Eleven 2000 using Emulator on my PC and it's basically the same game with PES 3. I will buy FIFA 2004 because it has lots of features but I also wants PES3 because of the gameplay. But if it is like this, sadly it's pointless as I couldn't hardly enjoy it playing in slow motion.
My PC Spec(yeah, i know.. it's old) :
Pentium III 1GHz (on windows xp professional)
384 SDRAM (PC133)
Asus GeForce 2 GTS 32 MB (latest 45.23 detonator driver)
Creative Soundblaster Live! 5.1 SE
Thanks.