Need some advice before I upgrade.

I'm confused if the PSU i have can handle the upgrade i want to make.
My current system:

-Apevia APEVIA X-TELSTAR-JR G-Type X Steel ATX Midtower Case
http://www.newegg.com/Product/Prod [...] 6811144211

--APEVIA ICEBERG ATX-IB680W-BL 680W ATX12V / EPS12V PSU
http://www.newegg.com/Product/Prod [...] 6817148028

--AMD Athlon X2 5000+
http://www.newegg.com/Product/Prod [...] 6819103211

--4GB DDR2 800Mhz OCZ TitaniumRam (Timings are 4-4-4-15)
http://www.newegg.com/Product/Prod [...] 6820227270

--Asus M2N-SLI Deluxe Motherboard (nForce 570 Chipset)
http://www.newegg.com/Product/Prod [...] 6813131013

--Nvidia GeForce 8800 GT 512MB Video Card
http://www.newegg.com/Product/Prod [...] 6814143118

--Western Digital 320GB Hard Disc Drive
http://www.newegg.com/Product/Prod [...] 6822136098

I was thinking of upgrading to a 6400+ (http://www.newegg.com/Product/Product.aspx?Item=N82E16819103228) and if possible another 8800GT in SLI. Is this possible on my current PSU? Any help would be greatly appreciated.
Thanks in advance!

Thanks for the advice, but I'm actually trying to not upgrade my PSU if possible, I just wanted to see if what I had could run a 6400+ (i know its a 125W, 90nm CPU and my current one is a 65W, 65nm - so I assumed there would be a jump in power demand and I really don't wanna fry my system) and if it can run one then if its possible to get another 8800gt in SLI along with the 6400+ or would that be overkill on my PSU.

I'm aware that it isn't the best PSU but it was cheap, looked great, and was SLI ready so I though it was a good purchase at the time. Sorry if my questions are confusing I'm not very good yet with PSU stuff, this was my first build so I'm new to this.