|Ubuntu 8.04 desktop... remember ;-)|
So, as a humble advice, you should consider upgrading into the latest LTS version of Ubuntu which is the 10.04. In that case you can read this post for further instructions. Or, just make your backups and install a fresh version of Ubuntu 10.04 or the latest 10.10 (not LTS).
If you use the 8.04 server edition however, Canonical will still release major bug fixes for it nonetheless.