Best way is to get bigger drives, SCSI to match your existing ones, large as possible with the controller/mboard
then use something like StorageCraft Shadowprotect (acronis will do it too) to image the drives to USB,
put the new disks in, re-create the array,
Boot from the Shadowprotect CD, use it to create a C drive of at least the size of the old one, restore the c partition
You will probably have to reboot again, boot from the CD, then create an f partition of as large as possible, restore the f partition from the image you took earlier. Done.....
If you have a problem and need to put a new disk controller in etc, then the above product will allow you to do a HIR (hardware independant Restore), and insert the new drive controller drivers to prevent you getting a HAL error as soon as you try and reboot.