Depending on your hardware you should be able to boot fine into multiple OS's across three drives. All drives seem to be IDE, so you would need two channels, but perferrible four to do so. In fact it simplifies things when using a Grub loader to select which drive to boot from after POST. However, if your building a new PC, I would still get at least one SATA drive in there for your primary OS, IMO.
Another note on the Channels: IDE drive (2 per ribbion) will only transfer data at the slowest speed. So if your ATA 133 drive is shared with your CDROM drive, odds are youll only see DMA 66 at best. So maybe a 20 dollar PIC IDE controller might help you out some more.