It is coming to the PC, Sony just aren't allowing it for the GC or X-Box - ever. Much like GTA3 for the PC, I doubt we'll know exactly when Vice City is due until a month or two before its release, but yes, Sony say it is coming.
Ignore the notice on some websites, it's just like MS said Splinter Cell would only come out for the X-Box, yet we've always known that is was headed for the PC. I’d guesstimate Vice City on the PC for late spring.