Also, just to keep it interesting... maybe...

Look up 'FretBoard Warrior' on google - a little flash game that flashes up notes and string numbers, and you then have to click the right fret.

When i was memorising the fretboard I had a set of 12 cards.... fret number on one side and the notes of all strings at that fret on the other... we didn't have computers in them days... ;)

It worked though... and for the love of God don't go for any of the sites/software that promise to teach you this for a fee... (fret2fret rings a bell here)... they're nothing beyond memory techniques and mnemonics.