I was recently in the same boat. I got the same camera, same kit lens, plus the 75-300 zoom. That was in December. A month later I purchased the "Thrifty 50" 50mm f1.8 for $75.
What've learned since then:
1. open apertures (smaller f-number) give better low light pics and often don't need flash. So smaller f-numbers are generally good when light is low.
2. If you want to capture something "freeze frame" where there is lots of motion then you want faster exposure times.
3. get a book on basic photography so you understand aperture, exposure, depth of field, ISO, etc.
4. play with the different settings to understand the effect they have. Choose aperture priority and shoot several pictures with different settings and look at the differences. Do the same for shutter priority and ISO settings.
5. Get big cards. I have 4 cards, each 8GB. Why? See #6...
6. Shoot RAW. It captures the most information and lets you do the most processing with a program like....
7. ...Adobe Lightroom. I use this on PC and its great. Handles RAW, good for organizing and basic image processing.
The important thing is to just get out and shoot. Remember what settings you used and see what effects those settings had.
NEVER SHOOT FULLY AUTOMATIC! IF YOU WANT FULLY AUTOMATIC, PUT THE XTi ON EBAY AND GET A POINT AND SHOOT!
The camera will bring you more and more joy, the more you learn about it. I am just scratching the surface and I'm ecstatic at the pics I've been able to take so far.