In task manager the CPU utilisation of your two CPUs./slant  cores is  shown
as one value covering the totally of both cores are is they were one  If you
select to show the utilization of the CPUs separatily you will see the
separete utilizations instenstead of the combined utilization.
As you are probably aware of very few home user Windows application programs
can concurrently use separate CPUs to perform a process...For example Spell
check in current MS Word will never make use of more the 1 CPU.
To find out if your Vista sysem is properly recogniizing the exisence of
both cores try right clicking on some process's in Taks manager and see if
both CPUs are checked as available under the  "afiiity option" if they are
both availble then your system is working correcetly.
Applications that currently can currently use multiple CPU;'s are limited
mostly to DBMS programs and some video file format conversion applications.