Microsoft has admitted to never using VSS on any of their internal projects (can't find the reference right now though :/). I used it for two years and it was stupid bad. Database was corrupted at least once a week.
Also, one of my favorite things to quote to VSS users is the first quote on Eric Wadworth's page, reportedly from someone at Microsoft:
"Visual SourceSafe? It would be safer to print out all your code,
run it through a shredder, and set it on fire."
Definitely go with SVN. VSS is like the nightmares of 1000 demons.