I hope you are talking about a separate drive not a partition right? At least make it a separate VMDK to put your data / logs / applications and maybe even another for swap. Differrent luns even for ultimate performance, even put vswp on another drive still..... seems like a lot, but if you are going to do it, do it right the first time.
For those of you counting that is 4 drives (4 distinctly different VMDK files). There are white papers on this for SQL performance on MS site, and they recommend this for physical machines as well, so VM's should not be any different.
That's how we setup, especially for SQL, spread out the love.... otherwise you may have performance issues.
