I'll spare your the details, but I have unintentionally ended up with a 4 drive RAID 5 volume, 3x 500gb plus one legacy 180gb drive
I don't think you have a 4 drive RAID 5 I think you have a 3 drive RAID 5 with the one legacy 180gb drive being the OS.
Please check your setup or post pic of how your setup is.
If you really did have 4 drive RAID 5 setup with 3x500GB + 1x180GB your space would be 540GB and using Matrix RAID to use the rest of the space to get another 640GB out of it, where a 3x500GB in RAID 5 would give you 1TB.
The 4 drive RAID 5 setup as listed above it is not possible to reduce the RAID 5 without running it as degraded for the 540GB space.
I decided just to buy 4 new 500GB disks (so cheap), configure in Raid10 on the Intel Matrix SM and then to re-install Vista. Fortunately I have a backup of critical files for retore.
The original failed Raptor disk that caused my learing the hard way is being replaced by WD - still waiting on delivery. Once i get it I'll configure the two original Raptors in a raid 0, and use for apps, swap space, and non-critical support files that need faster read.
Currently I have the Raid10 aray up with OS re-installed. Seems to work well but boot times are uninspiring, otherwise good performance.
My DVD is a sata drive so was forced to add an IDE DVD drive to load OS, b/c Marvel sata driver would not load in Vista install program, not sure why. Once OS installed, I loaded the Marvel drive np and sata DVD drive works fine.
Only piece not working is the 3.5" floppy. Died for some reason with drive light always on. No biggy, and not sure how to troubleshoot.
Good learning exercise overall, shame it had to be so painful, lol.