Is it 220 V? Or 240 V? I thought 220 V was the European standard. 240 V and 208 V are US standards, but not as common in the household as 120 V. Ignoring the 208 (three phase), I think some appliances in the house do run off of 240 V, like stoves etc.
So, do you mean 220 V, like a European enlarger would be equipped with, or 240 V, which I guess a heavy duty enlarger might be equipped with if it had serious power needs? If the former, the power supply might have a switch on it to operate at 120 V. If it's just a standard tungsten bulb with no supply, it should be fine even at 120 V. Or get a US bulb for it. If it's got a projector bulb and/or power supply, look for a 220-120 adapter like Ian mentioned.
If it's 240 V, then look for a US 240-120 adapter.