Windows 7 Parallel install Guides: What's this all about I hear you ask (Well probably not), well a parallel install guide is when you take your new operating system (or Old one if you are doing a data recovery exercise) and install it along side an already present operating system, in theory you can run as many operating systems as you wish as long as you have the hard drive space.
Parallel installs are very good for uses like data recovery, testing a new operating system, or to keep your old operating system in place will you migrate to new (As I always do), plus if you parallel install and find Windows 7 doesn't like your favourite piece of software, then you can simply boot into say XP and work with it there.
On my desktop computer I run XP home, XP Pro, Windows Vista 64 bit and now Windows 7 64 bit. Each Operating system has its own independent hard drive (You can use partitions if you wish, but its not recommended).
This best way to do multiple parallel installs is to start with the oldest operating system, and then parallel install in order of age, finishing with the newest. There is other ways of doing this but this is not the place to go into such depth.