I am going to be running two sets of hard drives in my new build. I will have two SATA drives, and two PATA drives. I do NOT want all 4 drives running at the same time, as two of the drives are for xp and two are for vista. I have power splitters for both drives. Question is, can I leave all of the drives plugged into the mobo (DFI) and just disconnect the power so that I can “switch” between the sets of drives? Or do I have to disconnect them from the mobo as well when they are not in use?
Welcome to hardwareforums GreyKiller 
Yes, You can leave devices plugged into the motherboard even if they have no power.
You would be much better off dual-booting than having to remove your case to switch’s OS (I Have tripple booted in the past, from the same hard drive :P). Instead, you just select which OS you want to use from a menu after POST.
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Vista 
Wouldn’t touch it with a 20ft barge-pole, what do you want it for?
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I suspect a keylogger on the main XP hard drives. Right now, I have a vista drive and a pair of xp drives. I have vista installed because I love abuse, and my customers will be buying machines with vista on them soon.
So what I will have is a mobo with sata connectors, the normal pata connectors for the two hard drives and two cd-roms. If I can leave the drives hooked up to the board without supplying power…AND I will hurt niether the drives nor the mobo, I can run both sets without making too much of a mess. I should only have to pull the side off once a day, or, I can actually route the wires to a switch on the front of the case to put power on the proper hard drives.
As long as I can leave all the cables in place, a simple switch should enable me to utilize all four drives easily.
Thanks for your help.