This will be my youngest daughters 13th dance recital this weekend. She also competes several times a year so I can totally feel your pain.
With the XTi the best advice I can give you is get as close to the stage as you can. This will allow more light to get into your camera allowing a faster shutter speed. And you will be closer so you won't have to zoom in as much - allowing your faster and much more easily handled lens to work better for you.
I usually sit in the second row nearly ontop of the stage it feels like. Crank your ISO up to AT LEAST 800 - higher if you can stand the noise and don't plan on making large prints.
One of the reasons I got the Canon 5DM2 in December was for the amazing low light capabilities/high ISO for dance competitions and recitals.
I also never use a tripod - too much of a pain in the rear when you also have costumes and make-up. I have no idea how many routines your daughter has in the recital, but mine has 7. A tripod is not one more thing I am lugging around and trying to keep an eye on.
Here are some shots I took last spring year using the Canon 30D and the Canon 28-135 IS lens. My settings were - ISO 1600, F/5.0 shutter 1/125. They are still VERY noisy - but I usually don't print them and when I do they are never larger then a 4x6.
These are "ok" - nothing I am really in love with - but they preserve the memories.
These next ones were taken with the Canon 5DM2 and I think they are much better - but then again it has a lot better low light capabilties.
Christmas recital - Lens Canon 24-105L IS (again sitting in the second row) ISO 6400, F/5.6 shutter 1/750
From competition last month. Canon 5DM2 - Canon 70-200L ISO 3200, F/6.7 Shutter - 1/350 I was NOT in the front close to the stage - probably more like 15-20 rows back and I cropped these photos quite a bit.
Good luck. I really hope you got something you are happy with.
Until I got the 5DM2 I was very frustrated with the quality of my recital/dance photos. But sitting as close as I was able to and using a high ISO and fairly decent lens (although not super fast) I got stuff I could deal with.