MJPEG and XVID are two different codecs.
Neither are included in Vegas.
XVID should be downloaded from its own site.
There are several MJPEG options available, some free, some paid.
If you just need to decode MJPEG, the MainConcept Demo is a good free choice.
Soory it toock me so long to post my reply to this post.
Here is the whole thing.
I need my Movie studio 8.0 C to be able to open M JPEG videos and I do have a program called Format Factory and it will let me make XviD MPEG 4 videos in it but I need the codec.
So I found
Combined-Community-Codec-Pack-2009-09-09.exe
and it sould have all the CODECs for my computer to playback the files I say above.
Now if I can playback files does this meen I can open them in Movie Studio
In that document it mentions that codecs use "merits" to determine which get used first. Installing a pack you don't need may cause problems for existing codecs. This program can help diagnose codec merit problems: