I want to install Gentoo, is there any possible way of downloading all the packages for gnome (gdm etc) so that when I do an emerge it immediately starts to compile? What I want to try to do is download the necessary files, dump them in the portage folder then do an update of the files in that folder and then do an emerge for gnome. I don't have an internet connection and can't leave my pc where I'm going to do the install becuase the dl and compile of gnome is going to take some time I want to try and do it this way. Is this possible and if it is, how?

emerge has a fetch only (-f or --fetchonly) option that will download the required files to your distfiles directory (by default it should be /usr/portage/distfiles). If the required files are already there, you will not need to download things for the compile.

You should probably do a pretend merge to check for blocks. I think --fetchonly allows you to download regardless of blocks.

So something like:
I don't use gnome though, so I don't know about package name specifics.

And if you really want to be safe, when you have the time and also a network connection, maybe you should run this :

This will download once and for all, all the packages that your box need.