>>difference between c++ on windows and c++ on linux system?

Differnt compilers which have different header files for functions. Basic functioning and programming on a Win or *nix system will be the same though.

>>You need to know C before you start C++...
Not neccessarily. Lot of guys I know started with c++ and are doing pretty well.
But if you decide to learn C++ first some basic knowledge of C would also do well since C++ can accomodate C in it. Like Jabberwocky said "C++ is a superset of C"