Rainbowzz, you won't necessarily lose everything. If Windows has become corrupted then it won't start, but you can have your existing drive attached to another computer as a "slave" and then you will be able to read all our files. We did this not too long ago. Bought a new hard drive, installed Windows on that and set it as the main drive, then attached the failed drive as a slave. We now use the slave drive to save all our work (but we back it up on CD too!)
YOu may even be able to use the programs - there are lots on my slave drive that still work and I jsut set up shortcuts on my desktop to get to them easily (haven't them into the start menu yet but I know it can be done just haven't got round to it.)
hope this helps