The reason I said "multiple systems", rather than "dual systems", is because I actually have four versions of Windows on my rig.

I normally use XP, so that’s one, plus I have a brand-new version of XP for testing purposes.  I also have Vista and Win7 systems, again for testing purposes and writing guides and such.

If you want to select between Vista and Win7, or two of the same OS, then you only need one hard drive with two partitions.  A selection screen will appear at boot-up allowing you to select which OS you prefer.  One will boot by default after X number of seconds.

If you want XP in the mix, you’ll need two hard drives.  The XP system goes on one drive and Vista and/or Win7 go on the other.  The BIOS will determine which is the default boot drive.
 

First And Last Warning

If you’re brazen enough to be considering this, then I presume you don’t need the usual lecture on backing up files and all that.
 

WinXP

I have my two WinXP systems on different drives, with the second one normally turned off via a power switch.  I use it for four different things:

• If I just want to install one quick little program that I’ll never use again, I’ll do it on the spare drive rather than clutter up the main drive or go through the system restore routine just for one little program.
   
• If I install a program that I later want to write a guide on, and I want to make sure I’m looking at all of the settings as a new installer would, I’ll install it on the spare drive and write the guide as I go through the settings.
   
• The new Adobe programs are massive bloatware, installing more than (are you sitting down?) fifty thousand files if you install Photoshop, Premiere and After Effects.  So, I normally keep an older (v5.5) non-bloaty version of Photoshop on the system.  But every now and then I want to use some feature (rounding corners) in the newer Photoshop so that’s when I fire up the spare drive.
   
• Some programs just don’t get along, like Adobe Reader (the online PDF reader) and Adobe Acrobat (the PDF maker), both of which need to be associated with ".PDF" to work.  So, I keep Reader on the main system and Acrobat on the spare system for the occasional time I want to make a PDF file.
   

Vista/Win7

To set up the Vista/Win7 drive is very easy:

1. Slap in the Windows install disc, have it format the partition and install the first OS. 

• Boot up and make sure everything works.
   
• Run the installation for the second OS and repeat the above, formatting and installing it on the second partition.  It’ll automatically put in the ‘Selection’ screen.

The only tweak you need to make on your end is to shorten the 30-second delay on the selection screen.  Go to Control Panel, System, ‘Advanced’ panel, ‘Startup and Recovery’, ‘Settings’.  You can select which OS you want to be the default and you can change the time of the delay.

It’s strongly suggested you be careful with these systems and not rely on backup image files.  You can try both Acronis True Image and the Windows version, but you might end up with an unfixable boot error, and even programs that also copy the boot block back to the drive, like True Image, might not work.  The whole OS selection business is really sensitive and I’ve blown mine up a few times.  I spent two hours using the ‘Repair’ feature and trying all kinds of ‘fixboot’ and ‘fixmbr’-type commands and nothing worked.

My own feeling is that the C Drive is much too important to screw around with boot blocks failing and such, so I keep the system on one drive and use the second one for multi-booting Vista and Win7.  That way I’m assured True Image will work on the main system.