HTC Droid Incredible and similar HTC devices with internal storage have an incompatible internal storage implementation.
That's why VidTrim does not show videos stored on the internal storage. But it should work normally for videos stored on the external Micro SD card.
So I recommend that you set your camera application to save videos to SD card by default. You can do it by opening up the camera app, tap the button on the left of the screen. This should bring up the options and you should be able to set where to save the video files.
If you already have videos in your internal card, please download ES File Manager from Android Market, and move your videos from internal storage (which is /emmc on Droid Incredible) to external storage (/sdcard).
VidTrim can also be directly launched by clicking on a video in ES File Manager. It will ask you to choose an application to open the video. Choose VidTrim and it will open that video for trimming.
If you own one of these devices, please e-mail me and ask for support. I can't do anything to work around this problem right now, because I don't have one of those HTC devices to test.