Shooting an event indoors - advice


So next week I will be taking photos for an event organised by a friend. I said I would do it but I'm actually kind of worried because of my lack of equipment. If it's not well lit I might have some problems.

Firstly I don't have any flash apart from the on-camera one (D3100). Would that be ok to use or should I avoid using it all together? I imagine it's pretty poor. Secondly I will have to use my kit lens (18-55) as the only other lens I have is a wide angle (10-20). The aperture on it isn't very wide.

I guess mainly my only concern is lighting. I have no idea how dark it will be but I imagine it will be fairly dimly lit.

Sorry if that's not much information to go on. Any advice would be helpful.