I have 2 computers racked up across the room in my computer room that I use in my office. They both work fine over a 50 ft vga Extension cable + Monitor cable. Same for the PS2 KB/Mouse. They say you can go about 75 feet maximum before the video starts getting flakey.
IDE cables can be a maximum of 24 inches. Thats it. SATA can go a bit further but it's still only like 5-10 feet (guessing). Why would you ever want to mout these away from the CPU/PS? Doesn't make any sense. There are solutions to remote mount storage, but they are expensive.
There are lots of places for cables www.atozcables.com is ok, just pick out what your looking for and search google for it.
USB you didn't mention, but it only works to 5 meters (16 feet). If you have to go further, then you need an active usb extension cable. They have them for 1.1 and 2.0. Here's an example: http://www.sewelldirect.com/USB2Exte...USB_2_Repeater