If you want to add them permanently, do the following. You will have to render the whole movie and re-compress it, but the dubs will be hard coded into the movie
Download VirtualDub, and open avi file.
Make sure your subs are in .ssa format. If not use SubResync which is a part of the vobSub program, to convert subs to .ssa.
Under the video menu in VirtualDub, click on Filters ( It will be grayed out if you do not have the full compression settings on.)
Click on add, and select subtitler, then it will prompt you to open your .ssa file.
Click on ok, and there you go......
This assumes you have some knowledge to set the compression settings yourself. I would suggest installing the latest version of DIVX, then you will be able to choose from the DIVX presets in the compression settings.
If you guys like, I will put up a tut.
pp