I use an old Dell 5150 Laptop that runs Ubuntu 10.04 LTS. The PC runs perfect with this most stable version of Ubuntu Linux. Just recently there have been a whole slew of Linux kernel updates that have become available for Ubuntu 10.04 LTS to fix some security flaws.
Most of the fixes concerned how the linux kernel handles internal packet traffic that could lead to a 'denial of service.' Other fixes dealt with privacy issues among users.
Be sure to get your Ubuntu kernel updated as soon as possible through the software updater. You can see which kernel you are using by opening up a command line and running this command: uname -a
A line in information about your system will return and you should see that you are running the kernel version: Linux-image 2.6.32-35 or higher.