One of the limitations of SQL Server is that it only supports 4 processors (as you can see here). That translates into 4 virtual processors if you run standard edition in a virtual machine. If there are more than four processors available whether physical or virtual then standard edition will only use 4.
However if virtualisation is something you are serious about then you also need to be aware of how SQL server standard edition is licensed when virtualised. Essentially each running VM that has SQL Server standard edition installed on it needs to be licensed as though it were a physical machine. The same applies to Workgroup edition, while Enterprise edition is licensed differently.
With Enterprise edition you license the physical server, and you are then free to run as many instances virtual machines as you want on that physical server. This could actually be cheaper than buying standard on larger server particularly with six and eight core CPU’s on the way (remember you license CPU’s not cores).
Also please be aware that all of this applies to any of the virtualisation platforms you can run SQL Server on, not just Hyper-V.