48c does seam a little on the high side for a mainboard temp

Has your motherboard got a northbridge fan or suitable heatsink ??
I'm running a AMD 2.8GHz Barton at the minute on a Gigabyte board with the northbridge fan removed (too noisey

) and it runs 24/7 - my mainboard temp is a steady 36c ........while the CPU is 45c
Could be worth a try increasing one or more fan speed to see if you get a significant drop in temp. As KraGorn says it is on the warm side and if possible would recommend trying to bring it down a bit.
You don't have any optimalisation programs or Overclocking utilities running do you. ??