MSP7 certainly is not garbage. In fact it is a very good NLE.
Sounds like dropped frames to me. Try,
1. Clear all TEMP files
2. If you are using a second hard drive then render to that. Also point your temporary working space to the second hard drive if you have one
3. Defrag all hard drives
4. Re-render your movie
5. Good luck
COMPAQ something or other with 500Gb Boot Disk, 1Tb external Firewire Disk, 4Gb Memory and a super duper sound card, 19" TFT Monitor etc etc etc
Sony TRV33e : Sony TRV310e : Canon XM2
Sony Vegas Studio editions to v11
Remember, there is always more to learn than there is to teach.