Replacement bulbs for e36

Ok I have found that there are many choices of replacement bulbs. Do I need to look for H1/H4s or HB1/HB4s? I'm trying to help a buddy out who bought new headlight assemblies but no bulbs, he is using the bulbs from the stock headlights now. He wants to buy upgrade bulbs but has read alot of horror stories of buying the wrong kind. He's planning on purchasing from www.rallylights.com (http://www.rallylights.com). If you all could direct me toward the correct model of bulb I would be very thankful.