Filled up my first 2 hds and wanna put another 1 in. My case has room for 1 more but I dont know what cable or where I can get one to hook up 3 hard drives. Can I use the floppy ide cable to hook up a hd or is there an IDE cable to run 3 devices on?

Each IDE Interface has two Channels, hence there are two ends to an IDE cable, and two ends only.

Nearly all motherboards have an IDE Controller with two Interfaces, which means a total of four IDE devices...unless you have two optical drives, then you should have space for one more. Bare in mind though, that the speed of each Interface runs equal to the lowest device. That means whatever hard drive you attach to the same Interface (cable) as the optical drive will run about 50% the speed.

If your system is newish, you may have SATA interfaces, which would be a better option. If you're out of luck on all those fronts, you can buy a cheap PCI IDE Controller card to slot in, and get an extra couple of IDE interfaces.