Salvador,

Unless you are running SQL Server 2005 Express (limited to 1 processor) or
have used  the affinity_mask option, it should use all processors available.
About affinity_mask:
http://technet.microsoft.com/en-us/library/ms187104.aspx

If you log onto your SQL Server box and run Task Manager, you should quickly
see (provided the server is doing something) that both CPUs are being hit by
the work.

RLF