Canon SLR Cameras

I’m planning to get my brother a macro lense for his Canon SLR 400D camera, but noticed that the 90mm ones are quite expensive, but saw that 50mm are a bit cheaper. Can someone tell me what the differences are and whether the difference is huge?

I’m using the Canaon Powershot S3 IS at the moment. It does the job but now I need a little more after learning to shoot manually. To go further I wanted to know which was a better camera between the two.

I’m not that much of a camera whiz, but I’ve outgrown my point and shoot powershot camera. I pretty much mastered it. Took great action shots with what limited options I had to work with, but its really time to step it up!
I need something I can take action shots of quads and portrait/action shots of horses.
I’ve really been torn between these two cameras. The Xsi and the 50D. I would really like to hear everyone opinions on these two styles of cameras.

I’m thinking about purchasing a Nikon d60 this week but I dont know if I should lean towards a Canon or Nikon? What is the biggest difference? Who has better quality? better features? Or whats your personal preference? Id really appreciate some thorough answers so I can make a good choice! Thanks guys!