SCT Controller described a potential conflict event and the possible contribution of minimal experience level at this very complex facility.

Narrative

Aircraft X had been cleared for Visual Approach into VNY. Aircraft Y was pointed out from the same Controller who handed off Aircraft X to me. When it appeared C172 was drifting further southwest into the path of the GLEX; I canceled the approach clearance and issued 4;000 and the traffic. Aircraft X reported responding to RA. I then rogered the GLEX pilot and said; 'when able; maintain 4;000; additional traffic; 737 five miles south of you; level at 5;000'; or something to that effect. Prior to issuing the cancel approach clearance; I asked the other Controller what the C172 was doing and that it appeared he was drifting southwest; I took RADAR; issued a heading to get Aircraft Y out of the way; and proceeded with traffic. Recommendation; we now have a greater number of controllers who have no prior experience in aviation working in this building. This was a situation where the VNY and BUR runways were turned around (normally 16 and 8/15; yesterday 34 and 26/33) and the lack of experience for the other CPC and perhaps the slightly less than 100% diligence contributed to the RA.