The Make Tech Easier site offers a short post titled How to Build a Lightweight Linux for your Low-End Laptop on why and how to use Debian to set up an older laptop.
I've used Debian many times to get old hardware running and, like the author of this entry, Joshua Price, I find the flexibility and lightness of Debian really helps the Linux distribution live up to its billing as "The Universal Operating System," which can run well on many different kinds (and eras) of hardware.
Like Price, I've done my share of minimal Debian installations, then building up the system with just the packages I need. That's especially necessary when you have a very small hard drive, like the 3 GB disk in my now-12-year-old Compaq Armada 7770dmt, which is running Debian Squeeze with Xfce right now.
Price sugggests running LXDE or Window Maker on your older hardware. I can't disagree about LXDE, which I'm testing now on what, for me anyway, qualifies as newer-older hardware, an IBM Thinkpad R32 with an AMD processor at about 1 GHz, 512 MB of RAM and a 20 GB hard drive.
While Price suggests unchecking the "Graphical Desktop Environment" box when doing the Debian installation, you'd be surprised at how well GNOME 2 in Debian runs on all kinds of hardware. For my 1 GHz-level processors (of which I have many at the moment), I think GNOME runs pretty well.
That means if you like GNOME, at least do an installation and give it a try. Do the same with Xfce, LXDE and anything else you might want to use. With every new hunk of old hardware, it pays to do a bunch of test installations before you commit to any one thing so you can see what works, what doesn't, what's fast, what's slow, etc.
So when an older computer enters your oeuvre, throw a bunch of operating systems and environments at it before committing to any one setup.
I'm a fan of LXDE. My Thinkpad would run great with GNOME 2 and probably does a little better with LXDE, but the point I'm trying to make is that GNOME isn't as "heavy" in practice as you'd think. This is GNOME 2.x I'm talking about. GNOME 3 is something I have very little experience with. But from what I'm reading, those with older hardware will be using Xfce, LXDE, Enlightenment and other window managers and desktop enviroments more and more as the GNOME Project puts 2.x in its past.
For a small drive, doing the installation Price's way -- minimal, then adding your desktop environment later -- is a good way to go. But if you have enough disk space, just use the LXDE/Xfce image of Debian, or pass the desktop=lxde boot parameter (or desktop=xfce) when you use a network-install image.
I agree with Price on the use of sudo. Ubuntu uses this by default, and it's part of the base install of OpenBSD as well. I think sudo is too good not to use.
Price also advocates the installation of PulseAudio. I'd say stick with ALSA for now unless you have some compelling reason to use PulseAudio, and on older hardware I really can't see any compelling need for PA over plain, just-works ALSA.