You can use the design at Oscars site for the Ipac LED Interface. 3 transistors is a lot cheaper than relays, and I doubt you need to switch 5 or 10 amps. a standard transistor should be good for a couple of bulbs. 1K resistor between the ipac output and the base of the transistor, 12V from the PC, (same connector pin on the other side) to the emitter, and from the collector, forget the resistor, go straight to the bulbs, then to ground (common ground with PC PSU.
Should be fine.
If you want to go with relays, forget a standard relay at 5V as it will draw more current than a led on the IPAC, you would still need the circuit, again minus the resistor on the collector to drive the relay. You could use a 5vdc Reed relay though, digikey is the cheapest at around $8-9 each, and they draw down around 15-20ma, which should be ok on the IPAC.
I'd just use a couple of transistors though.
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