WM11 Runtime slows down video decoding on everything - what to do?

[dragonfly]

TV-Server Version: N/A
MediaPortal Version: 0.2.3.0 RC3
MediaPortal Skin: BlueTwo
Windows Version: XP SP2
CPU Type: Athlon 64 3500+
HDD: 200gb ATA
Memory: 1gb
Motherboard: Abit AV8/3rd Eye
Motherboard Chipset: VIA
Motherboard Bios: Cba to reboot and check.
Video Card: nVidia GeForce 7600 GS
Video Card Driver: nVidia ForceWare 163.71
Sound Card: Sound Blaster Live24
Sound Card AC3: No
Sound Card Driver: Creative shipped drivers, updated
TV Card: None
MPEG2 Video Codec: ffdshow (atm)
MPEG2 Audio Codec: ffdshow (atm)
Satelite/CableTV Provider: None
HTPC Case: Ugly-as-hell Tower Case 2000
Cooling: A couple of fans
Power Supply: 540w
Remote: MCE
TV: 50"
TV - HTPC Connection: DVI -> HDMI

So here's my new problem: I just uninstalled the Windows Media 11 runtime, because it made all my x/h264 content desync with audio. This strikes me as odd because HD content should still be decoded by ffdshow if my setup is correct.
I think what happens is when I try playing HD content (h/x264 and/or WMV) in MP, the video isn't decoded fast enough and I end up with framerate dropping but the sound continues to play at a constant rate, thus resulting in A/V desyncing. Playing the same files in VLC works fine, but both in MPC and MP the problem remains.
So I uninstalled WM11 runtimes like I said, and that fixed the issue. The problem then is that I can't play WMV10/11 files without the WM11 runtime, so... I'm thinking I might need to turn off some processing functions in WM11 or possibly find an alternate decoder, but there seem to be none available yet, at least not open source ones.
I can't find anywhere to configure WM11 runtimes, neither in Windows nor in any player applications.
Is there any way to do this? Right now, I'm stuck with not being able to watch WMV10+ content because it bogs down ALL decoding on my HTPC, not just the WMV stuff.

Cheers!