In this case, it depends on who saw him first though, both of you can talk about it. Note that it would also depend on what they guy wants or rather who he is more interested in. If you think that your friend likes him more than you do, consider avoiding the guy so as not to ruin your friendship.
Just try not to turn it into a Sakura/Ino incident. If he's more important then she is to you... then I guess I'd say go for him, but ye, talk it over with her.. It might help clear up some issues between the two of you.
What I would do is let my friend flirt with him and, if shes lucky, go on a date with him. If after a while and she doesnt like him, wait about six months and then ask her if you can date him. If she says yes go on ahead. If she says no, wait a little bit then ask again.