How use info

["g.castaldi@gmail.com" <g.castaldi@gmail.com>]

Hi,
I like use emacs beacause is really powerful but a weakness I've found
is that the help, the info pages, aren't so easy to use.
For example now I need to find out how I can put a conditon based on
the operating system in my .emacs. I don't know where to look for but I
suppose that if I could search on all the info pages the worlds 'os'
and 'operating system' I found the right pages.
Instead, if I've understood good, with info I can only:
* navigate among the pages
* execute a search by index (i), I've tried several searchs but it
didn't find anything, even if 'emacs', 'command' and 'lisp' (I'm using
emacs 21.3 under windows)
* execute a search with 's', but it searchs only in the current node

I'm right or I haven't find the info command I need?
And if I'm right what do you do when you need to search an info but you
don't know where to search?

Thanks a lot.

Giannandrea