37c isn't bad at all, and the Asus probe warning setting is probably set too low. 37c is only 98.6F (body temperature), and nothing is going to melt or fry at that temp.
Check where you've connected that "optional fan", make sure that asus probe isn't slowing it down, that it's indeed running at 100%. Plus if it's a real small fan, you might be better off rigging a larger, higher output fan over that area for better airflow across all those components.
Also you need to verify that the temp diodes are being read correctly in the bios. My P5B temps are way off in the bios and windows for the proc. Coretemp95 reports my core temps 10c higher than asus probe reports them. So don't trust those two readings 100%. The coretemp95 reading is a lot more accurate than the other two.
Airflow is the best thing you can do for your motherboard. If noise is a issue, use a larger fan, like a 120mm, that spins a little slower but still puts out some decent air. Plus having as close to equal airflow entering and exiting the case is crucial. Leaving the side open helps, but also hurts. Heat can radiate away from the hot spot quicker, but all that openness also eliminates the case fans from maintaining airflow across certain spots of the board.
