Zooming with a DSLR

[DJM]

Ok thanks guys for the examples. Whats the sort of limit of mega pixels before a cropped picture becomes pixelated? I have been looking at secondhand Canon 40D, I believe it has 10 megapixels, would this be enough to prevent pixelation when cropping?

Does it come with a zoom lens?

I have just been looking at them generally and have not got a set camera in mind (looking at eBay and other secondhand photography resellers).