I wouldn't recommend CS4 specially if you're a begginer, CS2/3 are much more user friendly. As for backgrounds, ya can use stocks if you're looking for sumthin' simple, clickeh here:

SXC

It's a great site with lots of high quality stocks, lurk around n' get some.

You're also gonna need to learn the basics of sig makin', so I suggest learning from tutorials first before creating your own work.

Hope dat helps. :]