Change Clip Speed

'Export with Quicktime...' choose dv-stream
import to iMHD6 (previous)
and add Effect slow/fast/reverse...
export back to iM08 ...

Any advice?

Alternatively, if you have QT Pro, you can try the following:

1) Open the clip in QT Pro
2) Open the "Show Movie Properties" window
3) Select the Audio track
4) "Extract" the audio track by pressing the "Extract" button the in upper-left corner
5) Select the extracted audio track player and set in/out points equal to 1/2, 1/3, 1/4, etc. the length of the audio track (1/2 will double the video speed, 1/3 will triple it, 1/4 quadruple, etc.)
6) Reselect the original clip player and press "Commad-A" (to select the entire clip) and "Command-C" (to copy it to memory)
7) Reselect the extracted audio track, press the "Jump to start" button to ensure playhead is at the beginning of the audio clip and then use the "Add to selection & scale" Edit menu option to add the "scaled" original clip the the new player
8) Deselect or delete the audio track(s) and save the resulting file

While these steps may seem complicated, they only take a matter of seconds to accomplish. Here is a sample "double speed" file I made from a clip that happened to be on my desktop as I wrote this:

http://homepage.mac.com/jrwalker4/.Public/AESFastMotion.mov

So iMovie 've no build-in features for change speed/frame rates.

Not in iMovie '08.

Can i use MPEG Streamclip first since my source vro files have to be convert in streamclip first 2 quicktime mov

No. While MPEG Streamclip can change the number frames for a given period of time, it also changes the rate at which they are played back. (E.g., converting from 30 fps to 60 fps in MPEG Streamclip would create a file with 60 fps which is played back at 60 fps.) The simple technique I mentioned takes all of the original frames in the clip and compresses them into half the display time. Thus, the rate of playback is changed but not the original number of frames per unit of time. To better see what I mean, load the sample file I provided into the QT Player and observe the playback frame rate during play. While the original file remains 30 fps, playback is displayed at 60 fps. You can, in the same manner, playback a 20 fps file at 60 fps for 3 times the speed, a 15 fps file at 60 fps for 4 times the speed, etc. This is just a handy "trick" that can be quickly applied using QT Pro without having to run your file/files through a separate full editing application.

This technique works. I have used it to somewhat more, ahem, subtle effect.