Video playback in iTunes 7 and 7.0.1: it stutters!

Question

Since I've upgraded to iTunes 7 and now to 7.0.1, all my music videos and tv movies play at 2 (in words: two!) frames per second when played inside iTunes. In Quicktime and also on the iPod (5g) or the TV set with an iPod connected they are playing very fine.
It seems to me that this is a problem with mpg4 because the h264-encoded files play fine in the iTunes application. Is there a workaround to fix this problem? I have over 350 music videos and short fun clips in my iTunes library to synchronize with the iPod and I'll not encode them all again to h264 just because there is a bug in iTunes.
Oh, btw.: At work I use an iMac (Intel) with the same iTunes 7.0.1-library. All the videos (mpg4 or h264) are playing fine there. Maybe Apple is not testing on the G5 anymore?
Any help or comments appreciated!
Dual 2 GHz PowerPC G5   Mac OS X (10.4.8)  

Answer 1

The 3ivX codec is in your quicktime library folder, normally: root/Library/QuickTime, but I don't think, that Apple encodes their movies with an unsupported codec. Maybe there is another unsupported codec in your library that creates the iTunes-stuttering or the reason for your problem is completely different. I paste here the content of my library folder. If you have anything else in your folder, quit Quicktime Player and iTunes (if they are running) , remove the plug-in and try your movie again in iTunes. Hope, this helps.
Here's the list of my library content, that is working with iTunes 7:
AC3 Codec.component
ACTLComponent.qtx
AppleIntermediateCodec.component
AXELplayer.qtx
DivX Decoder.component
DivX Encoder.component
DVCPROHDCodec.component
EyeTV MPEG Support.component
FCP Uncompressed 422.component
ffmpeg DivX.component
Flip4Mac WMV Export.component
Flip4Mac WMV Import.component
KinomaExporter.component
LiveType.component
M100 Transcoder.component
Microcosm Decode.component
MP3.component
msmpeg4v2.component
OggVorbis.qtx
On2_VP3.qtx
on2vp3.component
QSXEssentials.component
QTFbx.component
Sorenson MPEG4 DecX.qtx
Sorenson MPEG4 PcktX.qtx
Sorenson MPEG4 ProX.qtx
Sorenson MPEG4 RssmX.qtx
Sorenson Video Pro OSX.qtx
Spectrograph.component
srtImport.bundle
Toast Video CD Support.qtx
XviD_Codec v0.5.component
Zoomify.component
ZyGoVideo.component