Hey all,

So my bands vocalist wrote lyrics for a very Sweet Child O' Mine style song, IE an up-tempo ballad - this is the first song of that type I've ever tried writing guitar parts for and am finding it a bit difficult as most of our other songs have been straight ahead AC/DC/Black Sabbath style rock. Obviously I don't want a carbon copy of SCOM, but any ideas how I would start about writing it?

Sorry for the lack of knowledge in this area!
try playing around with different scales until you come up with a cool lick, the build a song around it. thats my usual method at least
Seeing as we have only one guitarist, I'm not sure which approach to take - should I use a chord prog or a lead lick/riff used from a scale and leave the basic rhythm section to the drummer and bassist?
Since you don't have a lick you want to use, I would recommend that you start with a chord progression.

Harmonize the melody line. Do you know how to do this?

No you have a chord progression which gives you a foundation for your song. Coming up with a cool lick to go over this, to intro it, or whatever may be a challenge - but you have a song. It may be worthwhile to record a version of it with straight-ahead chords so that you can take it home and work on doing more interesting things with the guitar part on your own.

But if you start with a chord progression, that gives you a basis in functional harmony from which to build your licks. Most of the time, it's easier to write a chord progression and then come up with a way to "hide" that progression, unless you already have a riff in mind to build the song around.

(And when you do have that riff, you usually still need to figure out your chords as the next step, anyway).