yeah, there are usually a lot of services that you can disable with ubuntu, because in its newbie friendliness, a whole lot of stuff is active by default
i used this link to speed up my wifes box a lot.
another thing you might consider is the gnome thing. ubuntu uses gnome by default, but nothing prevents you from going with something lighter, like xfce4 or fluxbox. these are a lot easier on systems with less resources to work with. You will also get a slight performance boost with an optomized kernel.
uncomment the universe line in /etc/apt/sources.list
then do an
sudo apt-get update
apt-cache search linux-image
pick out a kernel that matches your hardware (IE pentium & higher = 686, amd k6 = k6) and whatnot.
sudo apt-get install whatever_image_you_like
then when you reboot, you will be using the kernel you just installed.
let us know if you have any problems