two problems: quicktime won't work in Riven, and sound from any DVD/CD

First problem:
I installed Riven, the older 5-disc version, a while back on my XP, and after much troubleshooting and gnashing of teeth finally discovered the 'run in 95 compatability' option and got the thing to run, but my quicktime movies don't have sound and it's beginning to matter.

Second:
Whenever I play Riven or a DVD or a CD, the sound skips. This does not happen with uploaded/downloaded music/movie files of any kind, nor does it happen with the Sims. I have not tried any other CD-run games.

Any suggestions?
Thanks!

Specs:
Dell Dim. DIM4600 Intel
Windows XP Home Ed.
Version 2002 service pack 2
Pentium 4 CPU 2.8 GHz
2.79 GHz, 504 MB of RAM

Disk drive: Samsung HD0406J
DVD/CDR: TSSTcorp