I have a Toshiba laptop on which I installed at first both XP-SP2 (SP3 gave me problems) and Windows 7. Everything worked perfectly fine. W7 is on Physical Disk1 and XP on Physical Disk2.
Recently, I installed Windows 8 in triple boot mode on Disk1. Everything was fine with W7 and W8 but the W8 installation somewhat crippled XP:
When I booted into XP in triple boot mode, it would start off perfectly and then get into a loop before reaching the Desktop screen (same thing in Safe Mode). So, through W7, I reinstated the Base Registry in XP. Now, XP goes all the way to a normal operational mode except for the WiFi link. I can communicate with the modem; it asks for the Connect Password, but once entered, nothing happens: there is actually no connection to the Web. Whenever I ask for the status of the connection, I get the request for the password + confirmation.
XP and 7 are all you need. Don't drive yourself crazy trying to get 3 OS'es on it.
I'm not interested at all in W8 because it's a disaster for the average user. It's installed only because I give introductory courses in IT and I want to be able to answer questions coming from the unlucky and/or "ignorant" guys who bought it.