"Attacking the people trying to help..." Help me out here; I need additional clarification.
If you read your posts back to yourself, you will see that a little too much anger is being directed at the anonymous people who are about to help you for free using their spare time. Already you have said yourself you don't want to pay the rather small fee to turn Winamp Pro, even though that would directly be of benefit in this instance. As no one here is paid to help, then that rapidly shrinks the amount of help you will get.
Note here: http://www.winamp.com/help/Player_Features
you will see the Pro version includes native H.264 decoding. This is why you hear some reaction from in_MP4.dll. As you don't want to pay for that, you are going to be using the older in_dshow.dll.
"Any chance of posting an actual example video?" [waffle and excuses cut] That's over 10 minutes for the upload.
No link, then I can't help much. There is the choice of uploading the video to some free hosting like Sendspace.com or mediafire.com etc. These are free. Yes, it will take a little while to upload. But it is quicker than nothing. No point in zipping up your compressed video file as it won't get much smaller. A much easier answer is tell me where you are getting these videos from and find me a link at source I can test from.
Your answers to the drag and drop questions \ jam questions \ etc. Confirmation of videos running fine in Media Player Classic, etc are useful as that means I don't need to look too deep there.
The swapping you did of in_dshow.dll and in_MP4.dll are useful to know. Mainly because this is where we will be concentrating - once you have supplied me with a video I can work with.
On my PC, I use the 32-bit K-Lite Mega Code Pack (as linked above by Evolution76). This is on a Vista Business 64-bit PC. I have Winamp Pro here, but to trouble shoot this issue I am hoping that won't make enough difference. My aim is to get you running through the in_dshow.dll.
I have just tested this on my PC and swapped the "MP4" between the two input plug-ins and it is working here happily on both. Trouble is the test file I am using is very different to your MP4 file.
When I am playing through the in_dshow.dll, I can see that ffdshow's audio and video filters have popped up in my task tray along with the Haali Splitter. Never changed any of the configuration of these, just accept the default of K-Lite's installer.
When did you last update your codecs? I know I don't have the very latest on this PC, but would be less than three months old.