system testing is nothing but a s/w  build testing.system 
testing is conducted in 2 ways.1.functional 
testing2.nonfunctional testing.
in functional testing the testers r concentrated on 
functionality of the s/w

system testing---once the complete application is developed
and it is installed into the environment then that is 
called system....testing of that one is called system 
testing...

functional testing----testing the functionalities of 
application is called functiona testing

the basic difference between them is in functional  testing 
the application is tested in the company environ ment
where as in system testing testing the application in 
client environment

ST : It is Blak box type of testing in which overall 
business requirements should be covered.

FT : It is also called as behavioural testing/Black box 
testing. Here test data derived from the specified 
functional requirements without regard to the final program 
structure.

Hope it may help.