Would it be possible, in windows 7 to parellel-ify the system, (run on many nodes at the same time for hugely increased performance) and would it be easy?
No. Windows 7 is designed to run better in multi-core system comparing to its predecessor (i.e. Windows Vista).
If you want some multi-node OS, you should try some special linux distribution specially built for this kind of usage.
The OS has its own methods for parallelizing O.S. operations, but not individual application performance. It is up to the individual applications to do any further multi-threading optimization (parallelizing). Modern OS's handle a lot of parallelizing currently as multiple core processors are now found in most modern computers, which require parallelization to be fully utilized/optimized.
As for making many nodes work together (Cluster), that is not a Windows 7 feature found on the consumer versions of Windows. Windows server machines have this capability for distributing network managment traffic, but not for individual client applications.
EDIT: Some links and parallel project:
http://www.lam-mpi.org/ LAM/MPI Parallel Computing - This is the LAM version of the MPI interface. I have used this before and it works well. Should install under most linux installations. I used this one with Ubuntu server 7.10. http://www.ubuntu.com/products/whatIsubuntu/serveredition
If you don't know what MPI is: http://www.mcs.anl.gov/research/projects/mpi/
Note: For this to work properly, the application needs to be adapted to the MPI interface or be built specificly for this environment.