Need some tips on shooting with 580 exII

My cousin asked me to shoot his theatre banquet this friday. I was comfortable doing it until he told me that was held in the "black box" room at our college. Its basically a medium sized theatre with celings roughly about 20-25 ft high, but everything is painted black. The walls, ceilings, the floor.. everything is black. He also told me it wasnt going to be well lit, pretty dim. So the only thing i have for lighting is my 580. I was wondering if a bounce card would be enough. Should i aim the flash straight up, or angle it 45 degrees? Or should I just direct flash? Also im sure the white balance will be screwy if i were to bounce if off black walls? should i just bring a white card, so i have a reference for correct white balance, or will the black walls not affect it as much as i think.

This is all the questions i can think of for now. Any advice would be greatly appreciated.

High black ceilings aren't going to work well for bounced flash. You can try it but I would be tempted to fire the flash directly to be honest. Use your 50mm and try to use the ambient light as much as possible.

If this is going to be something you do regularly then you may want to add some light modifiers and off camera flashes to your equipment.

Ceilings will be too high as you already know but you could try bouncing off the wall or you could either by a flash diffuser and use direct flash.. I have a Dome shapped Diffuser.. It is actually very good. and spreads out the flash..

I've no personal experience of such awkward shooting conditions - other than outdoors at night at a garden party. There I just used direct, unmodified flash and the results turned out OK (for an amateur). I've attached an example. There was nothing to bounce off except a pitch black night sky and there was not that much ambient light. This was shot with a 30D and 580EX at 17mm, 1/60, f/4, 1600 ISO, and was straightened/cropped and processed roughly in Lightroom.

Basically it sounds like you have nothing at all to bounce off, so you must provide your own bounce/diffuser on the flash head or simply use direct flash, as I did. Have a look at the http://www.lumiquest.c​om/ website to get some ideas of devices that will enlarge your flash area and not waste light upwards. Then see what you can find on eBay to accomplish the same sort of thing, or build your own. That should reduce the harsh shadows I got under chins.

EDIT : I've attached another example, outdoors, at night, with direct flash. It's not studio quality but the party crowd were happy enough. This was shot at 44mm, 1/60, f/2.8, 1600 ISO with the 30D and 580EX.

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So using an index card with the 580 ex wont help much either? I have a stofen, but havent been to satisfied with the results

I would say not. The point of an index card is that most of the flash goes up, to bounce, and a little gets sent forward just to fill the shadows in the eye sockets and provide a delightful catchlight. With nothing to bounce off of you'll be throwing 90% of your flash power up to the black ceiling and only 10% (give or take) forward. You need a modifier that collects the light into a large bowl and then throws it all forward., seemingly from a larger source than a little flash head.

Maybe something like this - http://www.lumiquest.c​om/lq881.htm, or similar.

Even something like this - http://www.lumiquest.c​om/lq925.htm, which I have seen versions of on eBay.

Over on the Fred Miranda wedding forum this seems popular - http://www.dembflashpr​oducts.com/flipit/ - the Jumbo version.

I should add that I have no personal experience of these. They just look like the sort of thing that I think would help in the conditions you describe. I have an eBay Omnibounce and that's it.

Another thing to consider - if you shoot portrait mode you will want to move the apparent source of the light to somewhere above the camera, even if off to the side as well. A direct flash will cast dodgy shadows to the side of your subject, rather than casting them behind the subjects and down, out of site. This might place the shadow directly in front of a face. A properly fitted diffuser will allow you to push the flash above the camera - either that or use a flash bracket.

The 580 EX II is a powerful flash unit, of course, but you should also be aware about that the guide numbers they list are computed assuming that there will be "normal" walls and ceiling to bounce from, even when the flash is directed towards the subject. Some light will bounce anyway, and help improving the overall illumination.
So you'll loose some light that way, and may not be able to get enough illumination on the subject without anything but direct flash.