Okay, here some informations on minimum load - the specifications are from a powersupply I found in a newsgroup, don't know the exact model nor this doesn't mean that values are the same for all supplies. Here we go:
Voltage __Current (in Amperes)__
Regulation Nominal V. Min Max Abs.Max Variance
+5VDC + 5.0 1.5 20.0 - +-2%
+12VDC +12.25 1.0 5.0 7.0 +-2%
+12VDC(Aux) +12.25 0.0 5.0 7.0 +-2%
-5VDC - 5.0 0.0 0.5 - +-5%
-12VDC -12.0 0.0 1.0 - +-5%
So what the heck does it mean? The +5V and the +12V on this supply must have a minimum current of 1,5A / 1A.
So you need to draw 7,5W on the 5V-line (that you don't want to use at all) and 12W on the 12V-line. Alltogether 19,5W + amount the supply wastes for itself. I'd expect 30-40 Watt all together, but I'm not that sure about this.
Problem is that you don't exceed the minimum load that is demanded.
Maybe you'll have luck with your power-supply, don't know, but look if there is a minimum current shown on your supply!

If it doesn' stated there this doesn't mean naturally that it'd work without.