I like my boot drive raided. Keep in mind that SW raid 5 volumes are not bootable.
I'd set it up like this:
sda, sdb, sdc, sdd
Partition all the drives the same:
sdx1: 512mb, sdx2: remainder of the drive.
Set up the RAIDs like this.
md0: /boot - RAID 1 using sda1, sdb1 (512mb in size)
md1: swap - RAID 1 using sdc1, sdc2 (512mb in size)
md2: / - RAID 5 using sda1, sdb1, sdc1, sdd1
I would use the Fedora emergency disc to set up and format the arrays. FC4, when using ext3, uses the defaults, meaning no stride and a 5% reservation for the superuser.
Terms to google: "Linux raid stride", "ext3 superuser", and "mdadm" ... you'll understand the importance! These concepts are worth understanding whether you go with your setup or my recommendation.
As far as hardware goes, don't spend a ton on CPU or motherboard for just 4 drives. Also, VIA chipsets are well supported and stable in Linux.