Quick info:
Raid 0 (Spanning/Stripped) is supported in every Windows 7 version (Beta/RC and RTM/Final) using software raid
Raid 1 (Mirror) is supported in Windows 7 Professional, Enterprise, and Ultimate (Beta/RC and RTM/Final) using software raid
Raid 5 is not support in Windows 7 (Beta/RC and RTM/Final) using software raid. You will need to use hardware (ie, a raid controller) or use a server operating system for Software raid.
WIthout doing any major testing – you will more then likly find a hardware raid controller (even using a built-in raid controller on your system board) will perform better then the software solution. Software Raid may perform faster if your hardware controller is using outdated technologies.
Software raid in Windows 7 is dependant on using Dynamic Disks. Because the Windows 7 does not give you a chance to create a disk as dynamic during the install process – you will need to do this afterwards. As such – you will need to install Windows 7 on a single non-raid disc and the convert it to dynamic / add the extra drive after you have installed the OS. I suggest you perform the raid adjustments fairly early after installing Windows 7 to ensure you either get performance (Raid 0) or reliability (Raid 1).
Above: RAID0 example using Windows 7 – showing the disk management screen plus properties on the hard drive
Please note there is no Mirror support in Home Premium (and earlier?) (Thanks for Jim’s comment)