Ubuntu 8.04?
Open the Synaptic Package Manager (under Administration in the System Menu at the top of the screen), and hit the "Reload" button. Then close Synaptic Package Manager and try again with the following guide:
Instructions for installing BlitzMax on Ubuntu 8.x
If you're still having no luck, can you tell us what is checked in the first tab when you go to System->Administration->Software Sources?
Open the Synaptic Package Manager (under Administration in the System Menu at the top of the screen), and hit the "Reload" button. Then close Synaptic Package Manager and try again with the following guide:
Instructions for installing BlitzMax on Ubuntu 8.x
If you're still having no luck, can you tell us what is checked in the first tab when you go to System->Administration->Software Sources?