Well................................, if you're creating a RAID 0 array, you're going to have to create your array first. Also choose your chunk size first. I've never heard this referred to as "chunk size", but as cluster size. But we're talking about the same thing.
If you start the OS install first, you will be copying files to your HD. If you then create your array, you will be wiping out everything you've copied. It's the same with the cluster size. Changing the cluster size on an existing array will necessitate a reinstall of your OS, programs, etc.
Boot up and enter the RAID utility using the key combination that appears on the screen. Choose performance, or RAID 0. Choose your cluster size. I would then reboot and verify the successful creation of your array.
Make sure you have the drivers for your RAID controller copied to a floppy. Boot off your XP CD. You'll be prompted to press F6 to install those drivers from the floppy. You'll be asked about partitioning, formatting, etc. Files will be copied, just as in a normal install. Keep those drivers handy, as you will most likely be prompted for them again. (Every install I have ever done has wanted them again).
You may have to play around with the boot order in the BIOS after your OS install is completed. The RAID controller will most likely be recognized as a SCSI device.
I'm no expert either, but the several RAID arrays I have set up have been done in this fashion. The best that I can remember anyway. I don't do this on a regular basis.