I recently purchased a 700W psu that states it is "Sli Certified". But, i recently purchased a motherboard that i would like to use with ATI crossfire. Would the 700W psu work with this?  

    As long as it has the connections it should, it would be extremely rare for it not to.  Crossfire and SLI certifications mean nothing, only in a very few cases there are some PSUs that just do not work right for whatever reason.  I highly doubt you will have any problems, especially if it is SLI certified

It will run fine. Stuff like "sli certified" are just like "vista certified" - marketing ploys that denotes no real difference in hardware specs.

^Agreed.
 

I haven't built a computer since 2004-2005, so i wasn't aware. Thanks for the great, polite and helpful answers.