Motherboard DG33 for Core2Quad Q6600 : Power Consumption question

Hi,

I have this motherboard installed with 2 GB RAM, a 250 GB Seagate
Baracuda hard disk and LG DVD RW drive.

My power-supply says its 450W. My UPS has a rating of 650 VA (should
be around 350 watts).

My display is also plugged into the UPS, which is a LG flatron 19"
TFT.

My UPS is not able to support my system during a power fluctuation.

my question is, how do I measure as to how much is my system using
from the mains ? That seems to be the only way I could decide on my
power usage and then only I can choose the right UPS configuration for
my system.

Please suggest...

regards
raghav..