It is possible to do this using something like TMPGenc.
There are guides at
http://www.vcdhelp.com. Somebody
recently posted here that he tried to do this very thing
using TMPGenc and he had all kinds of weird problems, but it should be possible. Another alternative that might actually be better for you is to re-author (re-burn) the SVCD as a "VCD". Many people have been able to fake DVD players that don't officially support SVCD into playing these discs if they burn them as VCDs. There was a pretty good post a month or so ago in this forum on exactly how to do this. Sorry, I don't know where it is offhand, but hopefully a search can find it. If you burn your SVCDs as a VCD, you won't have to re-record them, but you will have to copy the video file off the disc and possible demux it and remux it. Some people have had issues in copying video files off of SVCD discs to hard drives though where the copy
would fail to complete. I think this may be due to
the CD-ROM drive timing out before the copy finishes.
I hope you don't have this problem, but if you do, it's
a bitch to deal with. Nero contains some drive tools
that might help you to change the timeout value of the
drive. I could never get that to work, so I had to
resort to using a Windows version of the Unix "tar"
command to copy the file. If you know Unix, you
can download the Cygwin toolkit and figure it out
(
http://www.cygwin.com). If you don't know Unix,
you'll never figure out how to use tar correctly and
you'll have to find another way to deal with the
problem.