flash purchase? and learning technics?

Hi I have been shooting as a amateur for about a year. But after shooting many events and weddings for free/as a friend. I have a family friends wedding planned in the spring that I am going to be the main paid photographer at.

I own a Canon 300D, 50mm 1.8 , kit 18-55, and I plan on purchasing a Sigma 24-60mm f2.8.(would this lens work fine for flash work?), I also have a tripod and a remote. I have a 20G portable hard drive with card reader so I can keep on shooting.

I have done a bunch of photography in natural light and with a tripod, but I am very lacking when it comes to flash photography. Are there any books anyone would suggest?

Now to the equipment question. I would like to spend under or around $500. I would be doing mostly group staged pictures indoors, and some spontaneous pictures indoors at the reception. Suggests for a good set up? I do not mind what brand just something that works well.
thanks ahead of time for any responses
Paul

here are some examples of my work:

Two Sigma 500DG Super and a flash/umbrella stand. Shoot RAW and I hope there is some kind of PC/MAC to connect the card reader to ext HDD. Most Photo wallet don't usually require a card reader. Personally I prefer more CF then try to backup during an event just incase the backup is not successful. I generally carry about 7GB w/ me at all times. Shoot RAW for that "Just in case" situation. Consider the WASIA hack just so you can use FEC in camera, very helpful.

I wish I had the qualifications to help you out. You obviously have an eye for art. I think this is your best tool. This is what I am studying:
http://photonotes.org/​articles/eos-flash

Please share more photos.

Thanks...

It's always a little scary when someone books a wedding and then asks 1) what equipment he need to do the job, and 2) what books to read to learn how to do the job.

Thankfully you have a few months to practice. Sometime between now and then, please read this thread.

Curtis N, it is a little scary but I am good friends with this person and she know my photography. She is also a starving college student so I think the price I am charging is maybe the best she can do. But yes I plan on practicing a good in the coming months.

Randymays...thanks for the link and I will post a few more.

lostdoggy... My external hard drive is a handheld with car reader and I have two cards so hopefully I will be okay as far as that goes. Though I think I might buy a third before the wedding.thanks for the suggestion on equipment.

anyone have any other ideas of a good $500 flash sett up?

here are some more pics of mine: