Im upgrading my graphics card for gaming and just wondered if my power supply was good enough

My system-
AMD 64 X2 2Ghz
4Gb RAM
Nvidia GeForce 9800GTX+

I have a 550 Watt power supply

You would need to verify the power requirements for all of your components together, but it does appear to satisfy the requirements for your video card at least (taken from nvidia.com)

Nvidia GeForce 9800GTX+
Maximum Graphics Card Power (W) 141 W
Minimum System Power Requirement (W) 450 W

how would i go about doing that?, is there some sort of tool i could use?

Not that I know of. I used google and found a power consumption webpage for HDDs and one for CPUs (wikipedia actually), so you could do one for your motherboard and for each of your components.

With that in mind, you have a 550 W power supply, and based on your Video & CPU you have listed, if you have typical hardware (1 HDD, sound card is built-in to the motherboard, etc), 550 W should be plenty.

On the other hand, if you have a high-end soundcard, video capture card, and like a dozen USB devices, and other things I can't think of right now, you could (in theory) exceed that 550 W.

I run a 650W power supply with a Quad Core processor, 2GB RAM, 1 SATA HDD, USB keyboard & mouse, GeForce 8800 GTS and everything else is built-into the motherboard and have no problems.

My DVD-RW & Printer are USB devices that plug into the wall.

http://extreme.outervision.com/psucalculatorlite.jsp

You can try this to calculate power usage for all your devices.
Can you tell me which PSU are you having, because its not just the power ratings, but also the reliability you must look after for if you wish to keep your components healthy.

As I understand it the power available on the 12v rail is the critical measurement for graphics cards. Not the total W of the power supply.

Make sure your 12V+ rail exceed 28A.