Best practice is to use a dedicated fast disks for your tempDB.
The TempDB DB gets used by all the Databases as far as i can understand so there can be quite a load on it.
A 15Gb drive should be enough.
It is much easier to change the TempDB file location at installation but this is a step lots of people don't do.
Would even be better if you can split the TempDB's LDF and MDF files over different drives but this all depends on your budget.
When i talk different drives i talk about different spindle power...Different VHD's on the same hard drive defeats the purpose of this exercise
After this restart SQL and you are all-done