switching to GNOME
 

Can MEPIS use GNOME (Gnome?) instead of KDE? I have the impression that GNOME apps run faster, so I'd like to try it sometime. If I can, how do I install it?

apt-get install gnome

For some reason, that didn't work. It says:
Reading package lists... Done
Building dependency tree... Done
E: Couldn't find package gnome

My network is working...

lets see your /etc/apt/sources.list

I'll need to double-check when I get to my laptop, but I thought the package was "gnome-desktop"...

gnome is a meta package that provides the gnome-desktop meta-package, along with various other packages.

My etc/apt/sources.list says:
# See sources.list(5) for more information

# This file should be edited through synaptic
# New sources should be added only in the section at the end of this file!

# Primary
# deb ftp://ftp.us.debian.org/debian etch main contrib non-free

# MEPIS apt pool - specific packages available on-line
deb http://apt.mepis.org/3.4 etch main

# mplayer
# deb ftp://ftp.nerim.net/debian-marillat/ etch main

ah, your using 3.4

you need to uncomment the line that says:
# deb ftp://ftp.us.debian.org/debian etch main contrib non-free

to do that all you need to do is remove the #

you may also want to do the same for the other one:
# deb ftp://ftp.nerim.net/debian-marillat/ etch main

next do apt-get update && apt-get install gnome

Will it automatically overwrite KDE, or do I have to tell it to?

you will have both, then in kdm (where you log in) you can choose which one you want to use.