How to configure ubuntu for lightweight low-memory usage?

I just upgraded an old, secondary computer to the latest Kubuntu (10.10). It seems the effort was a bit too much for the hardware and one 512MB memory module died. I tried to take it away, clean the connectors, put it back several times, but to no avail.

Until such a time I can find a second hand DDR memory module, I am left with a meagre 256MB RAM, which is below the official requirements (384MB) to run Kubuntu/KDE. Indeed: the computer constantly swaps the memory, making everything painfully slow.

Since Kubuntu is already installed and I use it on all my computers (and I want to keep KDE for when I really need it), how can I configure ubuntu to squeeze out every bit of unnecessary memory usage?

This is a secondary computer but still very useful. We use it mostly for web browsing.

A "lightweight" tag is missing.

Kubuntu is really Ubuntu with a KDE desktop instead of GNOME. The lightest I know of is Lubuntu (lubuntu-dektop package) this is still running the same thing underneath Kubuntu and normal Ubuntu just with a lighter desktop.

The first thing I did was install XFCE4 and use it as the default desktop environment, instead of KDE. This I know is the single most important step I could take. It already makes a huge difference. The system is responsive again.

Still, the memory usage (as indicated by free -mt) is very close to the limit of available RAM, and depending on browsing usage, some swapping may still occur.

Please share other tips in other replies.

One thing that may help is setting up your swap partition for speed - with that little RAM, things will swap to disk and any RAM-based tasks become disk-limited. If possible, move your swap partition to a separate hard drive, and make sure it's reasonably large (3x your RAM is my usual rule of thumb).