pls kill your uncle for introducing you to linux. heh heh
pls read all of post and make your own decision.
ideally you could have just stayed with a good live cd/dvd if you lacked confidence to install linux?
1) since you have made changes...forget all of your old setup. its been changed so now irrelevant.
however bios does make a difference to raid detection and setup as most bios have a software raid cheat.
Therefore, you should be able to set your bios to ATA setting instead of raid.
2) use a linux live cd with a partition tool on it...command line or graphical....graphical is QtParted or gparted....to change all of your drives partitions and change the bootable flag for each drive.
3) as others have suggested......do ms first
put one drive....the 320G into sata slot 1 and assuming you have made it
c 100G ntfs
d 100G data ntfs
e (well xp won't see it) balance of drive...ext3 format
now put one 160G drive into slot 1 and 2 and 320 to slot 3
/ 20G ext3
/data balance of drive ext3
/ 160g ext3
insert linux install cd and install linux with grub to mbr (to slot 1 hard drive)
linux distros...good should find the bootable microsoft drive on slot 3 and give you a grub menu for it
if not read my signature....
4) the empty drive is partitioned as one partition ext3
when you decide to triple boot...the installer of a good linux can be used to change it.
each drive inserted must be modded by a live cd partition tool or by a linux installer partition tool...before you start the microsoft install and then the linux installs.
at a minimum you have
slot 1 bootable flag partition 1
slot 2 bootable flag partition 1
slot 3 bootable flag partition 1
do not let microsoft see any drive other than its own...sitting in slot 1 ...during the install process...its crap so can't handle non-ms formats
after ms is done...it goes to slot 3...then you insert both other drives and can format both in the one live cd boot using gparted etc.
oh....you need an easy to install Debian style distro not Ubuntu...try sidux? oh its a live cd/dvd as well