Hardware raid question (do I need a 4-port card)

I've got 4X60 GB identical drives that I'd like to use for home office
RAID in an XP server box. I've looked on eBay and found a ton of cheap
2-port IDE cards that claim to support up to 4 IDE devices. I
understand the RAID levels, but I don't follow how a card with 2 ports
can support 4 devices. Does it somehow detect and use the existing IDE
ports on the motherboard (which would suck for me since I already have
the OS on one of those ports)? Or does make use of two slave drives
(which sounds slow)? Any help or direction to a good resource is
appreciated!

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