Front derailleur problems

When I shift from the little to big ring, the chain mounts the top of the teeth for half a rotation.

Any ideas how to solve this?

Using Ultegra 6500 kit.

Sounds like it's not shifting fully perhaps due to cable stretch. Is there a cable adjuster on the downtube?

Aye there is - what do?

Edit: just double checked, pretty sure it's shifting fully.

Have you adjusted the limit screws? Could be that the mech's pushing the chain slightly too far out when you shift.
Also, do your chainrings show any sign of wear?
Park Tools have got a good page on mech adjustment:
http://www.parktool.com/blog/repair-help/front-derailleur-adjustments

Moved the outer limit screw a touch. Gonna go for a ride and see how I get on.

Also, one of the limiter screws on the back is a bit fucked - anyone know where to get spares?

Have you tried shifting with the bike stationary now you've made the adjustment? Probably best to get it spot on before you try it in anger :)

I've been making all adjustments while stationary, holding the rear wheel off the deck and shifting up and down while moving cranks with my hand.

If it's shifting better now you've probably sorted it - you just need to make sure you don't adjust it so far that it stops you shifting altogether or throws the chain.
I'm afraid I don't know where to get spare limit screws - LBS?

I might be able to spare a limit screw - I've got a couple of old 6500 derailleurs at home, sure I could see one go. Drop me a PM if you don't find another source

Might be a silly question, but does having friction shifting for the front derailleur mean I can change from a double to a triple chainset without any fuss?

Hingis - should be fine. Typically the range of the changer is significantly further than the range of the derailleur, so there's always some unused shifting capacity in the changer. So yeah, you'll be fine.