A CRJ200 Captain descended 300 FT into VNY airspace on a visual approach to BUR Runway 8 because he was unfamiliar with VNY's location and the Runway 8 ILS was OTS.

Narrative

I was the pilot flying; and we were on approach for Runway 8 in BUR. I had briefed the approach extensively prior to descent; and had slowed down to get configured with plenty of time to land on this short runway. This was my first time flying into BUR in a 121 operation; it was night VMC; and the ILS was OTS for Runway 8. I had loaded the ILS Runway 8 into the FMS to back up the lateral navigation for the approach. While configuring and slowing I was on the base leg for Runway 8; we advised SCT that we had the airport insight and we were cleared for the visual approach for Runway 8. Additionally; SCT advised us to maintain 3;000 FT until over VNY. Since I was unfamiliar with the area; I was looking down to verify the position of VNY; since it is not in our FMS database; and does not show up on the MFD. I could not identify exactly where it was on my chart; and as I was dividing my attention I found VNY visually. Unfortunately I misidentified VNY as BUR and thought I had gotten caught high on the approach while I got distracted. I began a slow descent until I could re-identify Runway 8 visually; and was currently showing a centered needle on the FMS for Runway 8. I lost approximately 200-500 FT below my assigned altitude of 3;000 FT just prior to VNY; and corrected due to my First Officer's quick recognition of my mistake (IE. I was thinking I was looking at BUR; but instead VNY). I immediately climbed back to 3;000 FT; and my First Officer helped me to re-identify BUR Runway 8. I got distracted; and was unfamiliar with the field. I was hoping the ILS would be working; as at night this would have helped me with orientation. I did not expect the 3;000 FT crossing altitude; and spent time heads down looking for an unfamiliar airport on the charts. I was somewhat mentally preoccupied with making sure I was on speed; and configured for my first landing at BUR; and extremely short runway; at night; with no ILS and terrain in all quadrants. My First Officer was my most valuable asset during this event. I feel I could have done a number of things differently; unfortunately; as is usually the case; I didn't think of those things in the 1-2 minute duration of the event. I could have told ATC that I was unfamiliar; and was not sure of the location of VNY. I also should have paid closer attention when briefing the approach of nearby airports in the immediate vicinity of BUR.