Creating More Light w/ My Rebel Ti

[cdm369]

I'm an amateur, and a friend has asked me to shoot their wedding photos this weekend. My concern is lighting, and up until now I've always used my Ti on "auto" settings and have been pretty satisfied with my photos. However, the area I will be shooting this wedding does not have the best lighting inside. I was planning on doing my best with an external flash during wedding shots, but for the portraits I'd like to utilize my manual settings on a tripod - perhaps shoot with a higher f-stop. I realize there are many factors here, but generally speaking is this the best approach for achieving better portrait shots or should I just rely on whatever I can get out of an external flash?

I'm looking for someone who can offer me helpful and practical advice. Please, no lecture or condesending thoughts on how unprofessional this is etc, etc. My friend is well aware of what they are asking and the expectation is accordingly. However, I would like to achieve the best I can for them with what I've got.

You suggestions will be greatly appreciated,

Thank you,
cdm369