Linux Install on RAID 5

I'm putting together an inexpensive NAS for my home network. My setup will be an LSI Logic MegaRAID SATA-6 controller in my box with 3 Seagate 320GB drives in RAID 5. I want to run a Linux distro (most likely Ubuntu for ease), but I'm not sure where to install it.

Should I:

1) Carve out a small partition from the RAID array for the boot sector/OS
2) Drop the OS right into the array
3) Install the OS on a separate physical drive outside the array?
4) Other?

In my WinXP systems, I prefer to keep the OS on a separate physical disk from my data/swap files - it keeps things more manageable, particularly in the event of hardware failures. This is my first venture into the Linux world and I want to make sure I'm setting it up the correct way because this thing will be holding a lot of data.

Thanks for any help you can offer.