I have a brand new amd athlon 3400 processor in my my new computer. The processor came with a retail heatsink and it said i need to use that one or the warrenty would void. So I put the processor on and put the heatsink on and everything went on right. I'm monitoring my computer and the cpu temp is at 63 C when its using 100% load. When it's not its has about 49 - 51 C temp. I ran Prime 95 for about 3 hours and the proccesor stayed at about 63 - 64 C with no errors. But now I installed cpuidel and prime runs at
59 C. So the processor is stable, it just needs to lower the temp. How can i lower the temp. I was told to remove the heatsink and get a nice one and put arcitc thermal compound on it. I think its just the retail heatsink is so crappy. It even came with a pad insted of paste. What can I do?

63C is normal for AMDs. Go to their website and they will tell you what the tolerances are.

Or get a better CPU fan. As long as you're not overclocking, you have nothing to worry about.

AMDs run hot. I have a 2500+ XP non-overclocked that runs around 44C under normal loads.

I had a 3200+ XP that I overclocked (until I pushed it too far.) But it typically ran around 65C

No use running CPUIdle, unless it is an Athlon XP.
For AMD64, run the Cool'n'Quiet option from the BIOS.

FYI, I run an AMD64-3000 with stock cooler at 39 C idle, 44-45 under load.
Cool'n'Quiet is enabled.
Case is Lian-Li aluminium with 2x80mm fans in, 1x80mm out, plus the 1x120mm out from the powersupply.
Case-temp 33 C, room temp 27 C.