Marco:
It depends how you have your computer set up and what program you are using, but yes, most programs download a photo at the same size it is stored in your camera - for example, a 6 mp photo is stored as a 6mp in your computer (unless, as stated, you have your computer set up differently). A 6mp photo can be blown up to a fairly good sized photo, though if you really want to blow it up big (say 20x30 or larger) my recommendation (for what its worth) is to use a photo lab. While this can be costly, it can also be relatively cheap at some of the online labs such as elcocolor.com ($9.95 for 20x30 on their internet special) or mpix.com - both of which do a fine job for a fair price you are not likely to match a local lab, I assume because of their quantity of work. I don't work for them or have anything to do with these companies, just like the results and they have good reviews for the most part on the internet. They pay for and use interpolation software which upsizes an image much better than most programs you would be using on your own home computer.