I'll try to help, I use a PC so I can give tips for XP. I'm indebted to Demandarin and Zwiller5 for their earlier posts which helped me solve the problem you're working on.
The trick is to get your clips into the right folder on your iPad, which (counterintuitively) ISN'T in the Videos app, it will be a subfolder in the Photos app that iTunes will create during syncing. So here goes, starting with the assumption that you've already converted your clips and are ready to sync them:
1. On your PC, create a new subfolder in My Documents/My Pictures. I called mine, creatively enough, Movies. Copy or move your clip(s) to be synced into this folder.
2. Bring up iTunes and let it connect to your iPad. (I have my iTunes set to sync manually so I don't have to wait for it to go through a sync cycle before I even get to what I want to do).
3. When connected, in the left pane click on the name of your iPad to open the window containing details about it. In the bar across the top of that window is a list of things like Apps, Music, etc. The last on on the right should be Photos. Click on that one.
4. In that window do each of the following steps: check "Sync photos from and select (as in my example) My Pictures. The first time you do this you may get a warning that all movies and music on your iPad will be deleted, do you wish to continue? As I had only 40 tunes and no movies, I said yes. Later is was a matter of a few seconds to resync the music. In subsequent video transfers this message hasn't appeared and no music has been deleted, only that first time. We'll leave the question of why music and movies need to be deleted to sync a few clips. That's for larger minds.
5. Next, select the radio button titled Selected Folders, then checkmark the box that says Include Videos. A list of folders in the My Pictures folder on the PC is displayed; checkmark the Movies folder (or whatever you named it) that you created in step 1.
6. Down in the lower right of the iTunes window, press the Apply button. The settings you made will be memorized and there should be a sync cycle. If not, press Sync (above the Apply button) once the Applying is done.
7. When the sync is done, open the Photos app. Press the Albums button at the top and you'll see there's a Camera Roll album and a Movies album (or whatever you named your folder in step 1). The clip you transferred should show up there.
8. It should also show up in both ReelDirector and in iMovie (if so it's high five time).
I've discovered that if I take a video out of the My Documents/My Pictures/Movies folder it's deleted from the iPod the next time I sync. If by that time you've already made a movie from it, that should pose no problem.
I'm now checking on whether there's a way to transfer clips without converting them. Others have trod that road before so I may be wasting my time. I did find that using this method earlier tonight I transferred an unconverted .mov file to my iPad and it showed up in both moviemaking apps. That clip was made in WVGA format in my camera, I'll see if I can get a 720p clip to sync.
I hope this helps, otherwise I just wasted a lot of typing--and your time.
