I recently upgrade my Gigabyte (GA-7DXR) mobo to Asus A7V333 and all other H/W is unchanged. My Athlon XP 1800+ is always running at around 30-35c with Gigabyte and CPUidle/MBM. After switch to A7V333, I noticed the temp stays at 50-55c all the time and goes beyond 60c when defregment my hard drive. Any idea whats going on here? Is it because the KT333 chip set or the new mobo? 50-55c is simply looks too high a number to me.

505 is pretty high...:)

50-55 C is nothing to worry about.
The first question about what's up is for others to answer. Why should the mobo and the new chipset rise the temperature with 20 degrees? Maybe there was something strange with your former figures (30-35 C) as this seems pretty low to me unless you have a lot of noisy fans.
For comparision my Athloon XP 1600+ (never idling - always working at 100%) runs at 55 C. Then it's put inside a box that is put inside an office box and then the office box is (except of the front with the hinged door) is inside a kind of cabinet. This arrangement gives me a nearly totally noiseless environment, and a temperature slightly higher than average.

I am assuming you got the temperature readings from the mobo diagnostics, either in the bios or a piece of software that came with the mobo.

Don't always trust what the onboard diagnostics tell you.

there is another possibility as well..

most MB temp monitor/sensors are not accurate at all.

I have 2 MB .. plugin the T-bird @ 1.4 G give different temp output!

Instead I bought an external LCD temp sensor
and measure it closely at 1 hour interval . and find out both MB with same CPU has very close temperatue

and yet one of the MB display 10 C higher than the other one?

hope this help!

you will know if your CPU overheat..

the HD crc errors, GPF will start to pop up all over the place if you don't get the blue screen of death :)

Yeah, I really doubt that the figure of 30-35 is accurate, because Athlon XP's are notoriously hot processors, and run mostly around 40-50.