How to figure what package will satisfy it?

[Bruno Buys <brunobuys@gmail.com>]

I'm trying to compile the new version of kradio, but configure tells me 
I lack X includes:

from config.log:

| #define HAVE_SNPRINTF 1
| /* end confdefs.h.  */
| #include <X11/Intrinsic.h>
| int
| main ()
| {
| XtMalloc(1)
|   ;
|   return 0;
| }
configure:28062: error: Can't find X includes. Please check your 
installation and add the correct paths!


I'd like to know what packages I need to apt-get, but more important is, 
i'd like to know what neat commands will let me search this by myself, 
so that this is the last time i ask this question...

Thanks all!