I used to have dedicated raid cards in my old workstation, one was SCSI and the other was IDE. In a server they are grate, supporting many disks and raid 5.
In my workstation the SCSI was good for reads and not bad for writes (140 MB/s WRITES) thanks to the XOR, and its the XOR, a dedicated processor used for "exclusive OR" calculations that makes a real raid card expensive.
For a PC these are complete overkill.
Yes there is a snappy-ness to the old raid 5 SCI (edit:2 there should be two "S" in SCSI!) set but with 10 disks at 10K rpm you would expect that to be the case.
I still use raid cards in my personal servers, doing multi disk raid 5 and one does 1TB of raid 10.
The other thing with Raid cards is they need bandwidth, you would need an PCI-E-8X/(4X at a push) or a PCI-X 100/133MHz slot.
conclusion with two disks not much point.
Some software like some Linux (Gparted?) cloning software could be used to image the running system to the new system, but install the drivers for the new card first so that when windows boots, it can use them. but you would need free disks.
3ware also have a SAS card now, don't know how this compares to ARECA or ATTO cards.
edit:: I have personaly installed an OS installed a raid card later, ghosted the OS to the new card (with drivers already installed in to the OS) and booted the OS off the raid card.
