I have recently rebuilt my pc and would like some recommendations as to ideal setups.
I have one IDE 200GB, 3x SATA 200GB, and 1 500gb Network Drive.
I would like to setup a RAID 5 config...to try out.

What im asking is what do people recommend having as a boot up drive - in particular reference to my current setup?

At the moment I have installed XP onto 1 xSATA, not using the other two drives. The IDE holds my old OS and some backup data. This config was Until i decide what setup to use going forwards.

I would like to ensure data integrity, at the moment my mp3s and Avis etc are stored on the network drive, but these are not backed up.
Would the best idea to use the 3 x SATA and backup to network drive?

IDealling i need some decent performance due to maintain streaming avi's throughout my home network.

Is it worth having the IDE as a OS boot drive, and then simply using SATA in RAID?

Sure, backup to the network drive seems fine. It should be unlikely that the backup drive fails at the same time as the other drives. Just make sure you use something more sophisticated than a simple copy, so you have several old versions of your files in case there's a creeping corruption (or some Word file where you find out you did some wrong edit a week ago or whatever). I use TrueImage in the same constellation.

If the time to boot Windows is of no concern, then yes, the IDE as boot drive is good, to take out the hassle of installing Windows on a RAID and just to make it easy in general.

The 3xSATA can be used in RAID5 if you like, but don't view it as a backup measure. Sure, it helps against a HDD hardware failure, but not at all against software failures (unwanted deletes, bugs, viruses etc.). Performance increase will depend a lot on what you do. Maybe a striping would be faster, but it would be best to just try out, I guess.