Buying A New Camera

[goldee]

I am looking at buying a new DSLR camera ( i have an old FujiS9500, looks like a DSLR but isn't one). I have used a Canon 500D and it was very good - some times it was a bit blury when i wanted to take 'action' shots of my dog running but i think it was more due to the settings i have it on.

I have also seen the Canon 550D which has just been released which as 18mp compared to 15. Is there any real difference in that? Are they just larger file sizes? Could you get bigger prints (poster sized) photos developed with the 18mp more so than a 15mp?

If any one has either of these cameras i'd be grateful to know how they are - the good/the bad.

I saw a tamron 18-270mm lens in harvey norman, which sounded great, but after reading a review it seemed that it was a bit on the slow side, so i may stick with canon lenses. I dont know much about lenses but is there one that is REALLY fast? (mainly to take photos of a very playful puppy!)

Thanks for any advice/help!

[rubiton]

My old 10D would do A3 sized prints with ease. The megapixels will not make a difference unless you want to go the size of a house (and then youd go raw anyway).