CS5.5 (version 7.5.x) is no longer sold by Adobe. You might find a copy on a site like Amazon, but be very careful about buying from unknown sources as it may well be either counterfeit or unregisterable.
@ Salah: Thanx, this is what I tried and didn't work.
@ Peter: You mean I can't download an upgrade I have to buy one?
Thank you anyway!
7.5 was not a free upgrade...