Welcome.
I have the predecessor to your camera the 1000d. It's a good camera for the price!
First off all in response to your question, Aperture is a good way to arrange your photos etc but doesn't warrant the price tag. I would look into Lightroom as it's simple interface makes editing photos really easy. However this is not a all out editing program for that you'd want Photoshop. Although if I were you I'd start with lightroom.
If you're going to take this relatively seriously I'd look at this book as a bit of bedtime reading:
http://www.amazon.co.uk/Understanding-Exposure-3rd-Photographs-Camera/dp/0817439390/ref=sr_1_1?ie=UTF8&qid=1325879248&sr=8-1It'll explain a lot about how the camera works and how you can get the best out it. Shooting in AUTO (green square) is fine but I'd suggest trying the semi-manual/manual modes. Auto tends to result in using the flash which can make photo's seem harsh whereas a longer exposure would maybe have worked out better.
For shooting rugby I'd look at using the Tamron with the camera in Tv mode, this will let you set the shutter time, which for sport would be higher the better. Probably above 1/250.
Also have a read of the stickies above as it may help you out!
Any other questions just ask! But read the manual and other sources on the net and I'm sure you'll get great results, sign up to FlickR (free) so you can upload your pictures.
Oh and this hobby can get expensive, very quickly
