[quote]have the OS on a different partion to other programs[/quote]
That never made any sense to me - if the OS then failed, the other programs would have to be reinstalled so why not leave them with the OS.
Partitioning is useful in that it will allow for an easy backup routine - if the OS and programs are on one partition (C), data like My Documents, emails, downloads etc can be on another (D), music and video on a third, and so on. That makes it easy to then backup the different data as you want.
Obviously it is an advantage to have two hard disks - and to copy data from one to another - an external one is even better.