Bow questions

my ranger/elementalist currently uses a bow with a fiery bow string. before entering a fight i use the conjure flame skill.

i'm thinking of buying thornbeard's horned bow. since this bow does lightning damage i assume i should now use conjure lightning for extra damage? also, once i use conjure lightning, does that mean i am enchanted? this bow does +15% damage when enchanted.

one more question - if i do not own factions yet, can i use a weapon introduced by factions? for instance, razorjaw's hornbow?

Yes, you'd want to use conjure lightning, which is an enchantment.

Second question: Yes, someone that DOES own factions can sell you the bow and you can use it.