I find that removing the side panel of the case allows my CPU to run cooler by 5'C. From 52'C Idle down to 47'C.

Is it possible that extra cooling or better fans than existing will keep it that low with side panel attached?

Yes.

Better room cooling will also keep those temps down. I ran an extra duct from my central AC unit to the room. This room is now as cool as the rest of the house and my temps are pretty consistant.

Yeah i just put an ac in my room and has lowered my temperature over 20*c. That and a new heatsink.

You'll also want to keep your heatsink clean too.. I recently cleaned off my heatsink from 5 months of dust build up and CPU temp dropped 12*C to 46*C from 58*C... That's what my temperature originally was, but the dust acts as an insulator and blocks air flow.

Rick is your comp over clocked?

Nope. It's an Athlon XP +1500 running at 1.33GHz as designed. The temperature only goes up a few celsius when it is overclocked to 1500Mhz or slightly higher.

I already lose 5'C with side of case off, I also found that with side on and a second 80mm rear fan sucking hot cpu air out also keeps it at 5'C less i.e. 47'C Idle/52'C Load

Check your PSU fan as well, if it is blowing into the case, I'd recommend turning it around so it blows out.

Keep the air moving from front bottom, to top rear. Heat rises, so it is only logical to help it to move in a natural flow.

yes, thus it makes sense to have some quiet 2900RPM fans at the top rear as I do and also a slightly more powerful fan at the inside front to push the air towards the mobo more.

Another ingenius way of cooling your PC is to have good ventilation in your room. For example, I find that even with a small window left open 24/7 during the summer can reduce the CPU temp by up to 3'C. This is most likely due to heat convection in the room where the hot air gets a chance to escape out of the room with fresh air blowing in. Thus the computer can use cooler air instead of just recycling the same used/hot air.

PS. the small window I leave open is not even in direct air flow contact with the case, i might get even more difference when i open a large window just above the case. If I feel cold from the draft then likely the computer will be as well.