installing software

i´m running linux on a very very small machine, with only a 100mb hd, therefore, i´d like to -must be- very selective in terms of what to install.
the distribution i´ve used is sleek to the limit, i don´t even have a text editor yet. i have to install some programs in order to do something, and since i´m new to linux, i do have some doubts regarding software installation.
i would like to ask you the following things:

* is there any program in linux that it doesn´t need to be compiled, like the *.exe´s in windows. if so, what is the extension of such program?

* what requires less hd space, to use source files and compile them -with a gcc type compiler-, or to use rpms?

* if i want to use rpms, what is the name of the program that ´takes care´of managing -installing, quering, removing, etc- the rpm files.

thank you very very much.