I think you’re better off with your current Celeron system. A lot of applications still don’t fully utilise parallel processing, so with msot tasks you’ll experience PIII 933 speeds while the other CPU will be more or less idle. Also more RAM and newer HD will give it the advantage.
I’d try both out, if you have the opportunity, and see which one suits you better. The emperical data would lean toward the Celeron having the advantage, but that depends on how hard you run certain apps and probably has the better upgrade path (unless you can run the Tualtin-core Pentium 3’s–the 1.2GHz with 512kB L2 cache or the 1.4GHz).