Tv-out video stuttering

[kampfy]

hi everybody,

i've been using vista media center for some time and recently switched to mediaportal. but until now vmc was the only piece of software that could provide stutterfree playback of divx/xvid content on my tv but only when used in fullscreenmode. when vmc was started it somehow changed the refreshrate of my tv and gave me stutterfree playback. any other player (zoom, wmp11 etc) and even vmc in windowmode resulted in stuttering playback (interval of about 1second).
since i have the same problem with mediaportal now, i hope someone here could help me resolve this problem

my system configuration:
AMD Athlon X2 3800
2Gb Ram
nforce4 Ultra MoBo with realtek ac97 onboard sound (using latest drivers for chipset and sound)
ATI Radeon X1800XT 512mb (using catalyst 8.10)
Monitor: Samsung 226BW (at 1680x1050 - 60Hz)
Monitor2: 32" 100hz widescreen TV connected via svhs tv-out (at 25i hz - 1024x768) - extended desktop - used for mediaplayback / mediaportal
Vista x86 SP1 with latest updates
mediaportal 1.0 rc3
latest ffdshow tryouts for movie audio / videorendering (tried different versions of ffdshow and other codecs for myvideos (pdvd7 etc.))

i did some research on the topic (actually been doing nothing else this weekend) and became more confused that i already were. although everybody says that evr should fix any refreshrate related stuttering it doesnt seam to work with tv-out for me.

what i tried so far:
dubbing a 25fps .avi without sound - result : same stuttering
dubbing a 25fps .avi without sound to 30fps - result : almost no stuttering

which leads to the conclusion: 60hz of my main display is a mutiple of 30 fps. so the stuttering must somehow be linked to the refreshrate of my main display although its not displaying the video. strange.

but i cant set my main display to 75hz (multiple of 25fps) to do a deeper research on this. catalyst only allows 60hz for my tft. so what the hell did vmc do to my refreshrate or whatever to resolve my stuttering issues?

anyone got any experience with this topic and is able to put me in the right direction ? any hint is greatly appreciated.

thanks in advance.

and: please excuse my crappy english. i hope i made myselve at least understandable