Hope this helps....
* re-install Windows 98SE and Matrox latest drivers (download it in matrox website).
* add the Prem50.ini in the Premiere directory (where the premiere.exe is)
* when creating a new project make sure that the resolution is supported.. (ex. 704 x 562, 704 x 480, etc.) Or just use the presets of Matrox.... (you can download it in the download section of www.desktopvideoworld.com) then add it in the settings directory of premiere.
---> By this time you should be able to capture, and open mjpeg files.
* If you're having problems with the preview monitor, specifically the target monitor... (ex. jumpy, distorted rendered timeline) trying switching to the single monitor mode..
* If you're getting an error when making the movie.... go to the audio settings and turn off the audio enhancement feature....
---> It worked for me
Hope it works for you guys too! 
btw, here's my setup...
PII-400, Asus P2B-B, 128 mb, g400TV, Samsung 3.2 gig hd, Windows98SE, Adobe Premiere 5.1 (using the RR presets).
don
* re-install Windows 98SE and Matrox latest drivers (download it in matrox website).
* add the Prem50.ini in the Premiere directory (where the premiere.exe is)
* when creating a new project make sure that the resolution is supported.. (ex. 704 x 562, 704 x 480, etc.) Or just use the presets of Matrox.... (you can download it in the download section of www.desktopvideoworld.com) then add it in the settings directory of premiere.
---> By this time you should be able to capture, and open mjpeg files.
* If you're having problems with the preview monitor, specifically the target monitor... (ex. jumpy, distorted rendered timeline) trying switching to the single monitor mode..
* If you're getting an error when making the movie.... go to the audio settings and turn off the audio enhancement feature....
---> It worked for me


btw, here's my setup...
PII-400, Asus P2B-B, 128 mb, g400TV, Samsung 3.2 gig hd, Windows98SE, Adobe Premiere 5.1 (using the RR presets).
don
