Hi, Blackecho posted a link about infra-red bulbs on one of the threads on this page - 'Heating Wooden vivs' by Deadmansfinger. I use a 75 watt bulb in a 3'x 2' x 2' with a dimmer stat, and my temps are fine - maybe a 60 watt would be better for your viv size, but if it's on a dimmer stat, the stat won't let it overheat the viv. BE should be along in a while, I imagine - he'll know for sure.
depends on how well the viv is vented but yeah 60 wat spot bulb should be fine. of course will need to be on a dimmer stat save it getting too hot, if the bulb dims alot all the time then you could try a 40wat it might be better :)