okay here is one you should try!
Hunter is totally right, practice with a metronome. Plays the parts from the songs you want to learn along with the metronome set at the right BPM. Here is an exercise:
Pick a riff or a lick that is medium or above medium in difficulty (even hardcore if you want a challenge) and set the BPM to a manageble tempo, medium to fast tempo. Now keep playing this lick or riff for as long as possible, before you loose consentration and falls of the timing. Annoying exercise, but it really gives something to your playing!