If you are doing RAID of more than 2 drives, you will need a 64bit pci bus or PCIe or whatever they call it now. 133 MB/s is not the actual or theoretical for a 32 bit bus. It's half that if you're lucky. The bus speed is 66 MHz Max for a 32 bit PCI bus. Server motherboards don't have 64bit slots for RAID for nothing. It's necessary.
The Areca is a good card, but I prefer GPL drivers that come with 3ware's new 9550SX controller. http://www.3ware.com/products/serial_ata2-9000.asp
. Kernel native, and hardware that's blazing fast for people with a clue, and with online RAID expansion. Which means you can swap out drives to a larger size and increase the partition size on the fly.
Hardware RAID cards are not expensive. It 2 port 3ware card starts at 100 bucks. Calculate the time that you'll blow on not being able to boot, and I'm sure it'll more than makeup for it in your lifetime.
If you want more bells and whistles like a battery backup for the controller, or more ports, or SATA II, yea- it'll end up going as high as 500-700 bucks for a top of the line card.
but you ain't looking at that if you are using motherboard software RAID. you just want it to work. Grab a 2 or 4 port 3ware and go to town. If you want to do RAID expansion or optional battery backup, get the 9000 series. If you just want it to work, get the 8000 series. In any case, I hope this helps.
Don't expect Nvidia to sell hardware RAID on their chipsets. They aren't in that business. It's too expensive for them and frankly it's for windows weenies that think they're getting something for nothing. There ain't nothin free in this world no matter how much you wish it were so. Good luck.