webcam cannot connect

I am struggling some time now to get my webcam working with live messenger: i
hope someone can give me some hints, maybe even a solution.
My pc is about 7 years old, the processor is AMD Athlon Model 4, with MMX,
without SSE. The operating system is windows XP sp 3. The webcam is a trust
WB-1200p, connected using USB. The webcam works with yahoo messenger and with
an application like splitcam, so i guess the drivers are ok (there are no
more recent drivers). I can also connect to the webcam using msn messenger
(previous versions like 5 or 6).
I cannot connect to the webcam with skype and live messenger 8.
What i would like to know: which subsystems does Live Messenger use to
access the webcam ? Is it possible that my directx is in error, or the worng
version ? Maybe some capturing driver/device somewhere, or maybe it is a
security feature that is not working properly. When i try to activate the
webcam the following happens: a green light switches on for about half a
second on the webcam, then it switches off and live messenger says it cannot
connect to the webcam because it is in use already, even if nothing else is
running.
I tried uninstalling/reinstalling components about a dozen times, but there
must be something that i miss. Could there be a conflict in language
versions in dll's or applications ?
I hope someone can help....