Hi Martin,

I know it sounds obvious but get a tubescreamer type pedal, none of the built in overdrive/distortion emulations are really in that ball park (do play with the governor effect though, it's really creamy sounding).

there are lots of tubescreamer type pedals about and although they can be expensive (£300+ for a hand wired job) they don't have to be I use a tc electronic "cinders" overdrive, its a nice copy of original tubescreamer and can be picked up really cheaply. It does look quite ugly though.

hope this helps

ali