Hey W,
Okay, here's my two cents: at 39C your mobo is a little hot, get two case fans- one intake(in front of case blowing in) & one exhaust(in back of case, under PSU, blowing out). My case runs at about 30C...........my case has 4 fans- 1 front intake, 1 side intake over cpu, 1 top exhaust, & 1 rear exhaust. My PSU is a dual fan 500 watt Raidmax(all aluminium).
Your cpu is also running a little hot. It should only be running at about 10C hotter than your mobo. What HSF are you using? I am using a T.I. Dr. Thermal TI-V77L HSF, it is not that loud. My cpu also a 1800+ runs at 40C to 46C, with the FSB set at 137 mhz.
If you really want to know how cool the coolest your system could run, take off the side & top panel of the case & put a house fan right up to the open panel.
The bottom line is: if your computer can do everything that you want it to, without locking up, it is running cool enough.................if you want all your components to last as long as possible, cooler is better.
By the way, I love that Shuttle AK31A mobo. It is the best low budget mobo that I have ever used.
Peace Out.....................tile
god knows your entire system setup & he would answer your questions if he could just stop laughing