Is there software I can use to find out my system's power consumption?

The reason I ask is because I have a 350W PSU that came with my Dell Dimension 8400 and I'm thinking of adding two more sticks of RAM (DDR2 533) and upgrading from a GeForce 6800 (no other letters, just a plain 6800) to either a 7600GT or an 8600GT, whichever is more powerful without blowing out my PSU. I've used the Extreme PSU Calculator a few times, but sometimes the calculations for what I already have go over what I currently use and there's a bunch of other variables I'm probably not factoring in. I thought that maybe a program that can gauge my power use and perhaps even give me more info on my PSU will help me make better decisions.

Also here's my setup to give you an idea of what I'm running just in case any of you were wondering.

CPU - 3.4 GHz P4 w/ HT
GPU - GeForce 6800
RAM - 1GB (2 x 512MB) DDR2 533
HDD - 160 GB SATA
PSU - 350W, Unsure of the amperage because it's in a bad place and the sticker is hard to see.
Floppy Drive (turned off in BIOS)
One CD/DVD Burner/Player
One CD/DVD Player
Wireless USB Mouse
Wireless USB Keyboard
Two USB External HDDs (not always on)
One 512 MB USB Flash Driver (not always in the slot)
One PCI NIC card (though I don't use it, I use the Mobo's jack)
One PCI Firewire card (haven't used this in a while either)
One 140mm (I think) exhaust fan blowing air from the heatsink out the back.
Parallel, Serial and Mouse's PS/2 ports are also turned off through BIOS.

Also the main use of this sytem is gaming at 1280x1024, but I expect that to change once I get a 1920x1200 monitor, though I doubt this will affect power consumption that much on the PC's part.