Two HDD's - best configuration?

[Father Ted]

Right I have two 250GB HDD's installed in my system.
Wondering what the best way to configure them for speed and reliability is.
Currently the Windows drive is just one large partition and contains Windows and my data, the other drive is partitioned into a 50GB drive for data backup and a 180GB drive for apps.
Could I organise it better?

 

[Father Ted]

what do you want, Security? Speed? Space?

Space isn't an issue, ideally data security is the most important aspect - my wife's degree course work to be precise. Data backed up to the second hard disk with occasional backups to CD should be good enough?
Also is their any advantage to having windows and apps on differnet drives - balance the load so to speak.