Before I started to use my 8051, I borrowed a book from the university library, written by Roland Dilsch, titled (translated) The 8051 microcontroller family, the original title is Mikro-kontroller der 8051-Familie. This is a very good book I think, it writes down the SFRs, ports, timers, etc., so I have read about it before I started to use it.
I've also read about debouncing.

I don't want to avoid C, but I haven't got much time now, but some weeks later I will start to learn C.
I've learned C already, but that was not much.
I've read about C developement enviroments, but I don't know exactly which is the best for AT89S52, please tell me the truth! Is KEIL good for me? What version you suggest?

And another (probably stupid question): If I would like to learn assembly programming of 8051, what's the software for it?

Thanks for everything!