45 degrees is fine, especially if you're not overclocking. I have a 1.33 (non-XP) T-Bird which is about the second hottest CPU ever produced - it runs reliably up to about 55 degrees with mild overclocking.

However, stock HSF combos tend to be either loud or useless. You might want to check out if any of the 80mm copper-based monsters will fit on your motherboard. These will allow you to run an 80mm fan at a slower (=quieter) speed and obtain the same or better temps.

After the CPU, check out PSU / case cooling. Some PSUs have rather loud fans that can be replaced with quieter versions (warning - high voltages can be present within PSUs even when disconnected - if you're not comfortably proficient, consider looking around for a quieter PSU). Case cooling can also be done with quiet fans. You can often get better cooling from 2 nearly silent slow case fans as you can from one loud fan.