I shot some photo's at a concert here at Purdue. I was jsut practicing with different light levels in an open environment. I first shot a few pictures with Av mode to see the images my camera shot and the settings it used. Then I went to manual setting and played around with the settings a lot to find a good setting. I used ISO 800 with these pictures, and the shutter speed is what I changed after picking the aperture to shoot with. Taking a picture, viewing it, changing settings were the steps I took.
Standing still might be an issue if you're after performance shots, but then again blurring can be desirable for this sort of shots - within limits. I recently attempted to take some photos of a friend's band live (the downstairs of the Betsey Trotwood, as anyone who's been there can confirm, is a small dark shoe-box somehow masquerading as a music venue) with my own compact digital, which is also only capable of 400 ISO and has a maximum aperture of f2.8 (the Powershot's lens is f2.2, right?). The results were totally unusable without flash, and with flash I only managed to get a couple of lucky shots where the guitarist wasn't blinded. Even then some serious Photoshop work was needed to undo the effects of the on-camera flash. Afterwards I realised I should have done two things...
1) Plan ahead! A tripod, something to diffuse the flash, getting in before anyone arrived to try shooting from different angles... any of these things would undoubtedly have resulted in better images.
2) Don't use a non-SLR digital.
The last one is debatable. A camera like that might be perfectly adequate - if you have the right lighting conditions. In this case you have been asked in advance so unlike me you have time to plan. In terms of composition, discuss with the band members what sort of shots they are after (but don't be limited by that - you may come up with something they didn't think of). Shoot lots and lots of photos, and then some more. Later you can get rid of those you're not happy with, and the band can choose the best from a good bunch. As for settings, a larger aperture (i.e. smaller number) is almost certainly better - though the image quality may be better slightly stopped down, e.g. at f2.8 rather than f2.2. I don't know the camera so can't really comment on that. Meanwhile faster shutter speeds are essential unless you want to blur for effect (e.g. to draw attention to the motions of the band members playing) but you generally wouldn't want everything blurred, so no exposures lasting several seconds, and don't even think of not using a tripod with shutter speeds under about 1/60th (higher if the lens is zoomed in).
Use the flash - that should help stop some of the action - even with a lower ISO. If I remember correctly, you can shoot raw with the Pro 1 (I don't use mine often). If so, you can underexpose a bit and bump the exposure in the raw processor. I don't usually recommend that but sometimes you gotta use the tools available to you. The biggest problem is going to be the shutter lag with the Pro 1. Great camera but the shutter lag will drive you nuts. Good luck
You are psyched to work in a studio! Try and get all the details of that set up. Once you have them you will be able to determine colour temp exposure and all that happy stuff. Try and show up before the band, so you have time to practice. The idea is too have the tech down so that you can concentrate on the shots.
Most important question I'd say is how well lit will the studio be? If it's not well-lit, and flash as you say will not be appreciated, then you may well have a problem. F2.2 at ISO 400 may not be fast enough without extra lighting of some kind. And if you have to go to the trouble of getting extra equipment to light the band, then it raises the question of why not simply borrow a more suitable camera (one with a faster lens, better image quality at higher ISO, no shutter lag etc).
I agree that the main question will be lighting. The next question should be what kind of "look" is the band going for. Stage lighting with lots of coloured gels or studio flash? Maybe window light and bounce cards? If the whole deal is up to you then what exactly do you have to work with? Is renting gear an option? Also consider the size of the studio. Will there be time constraints on the shoot?
As for what kind of look the band wants, ask them to give you as much information as possible. That might include looking at other album covers or photo shoots for inspiration, making sketches etc. Good communication between you and the band on this is vital.
Hmm, I'm not sure what else to suggest. If you can't use flash, your maximum ISO is 400 and the maximum aperture is f2.8, I think you're going to have a problem. You've got five band members and will probably need to take individual as well as group shots from various angles, so you can't really just stick the camera on a tripod, yet you cant really shoot handheld with regular indoor lighting and that camera. All I can think of is either get a good lighting set-up in there (though this too may be distracting to the band), or borrow another camera.