I want to get a rough idea of how long it's going to take to download a particular file. How would I go about doing that?

Pop along to Martindale's file download time calculator, enter the file size of whatever it is you wish to download and click on either the 'KB' or the 'MB' button, obviously dependent on the way in which you specified your file size (whether it was in kilobytes or megabytes). Now scroll down the table of time estimates until you reach the entry which correlates to the speed of your internet connection to discover how long you're going to have to sit twiddling your thumbs waiting for your data to touch down. Give the man a cigar, he's a genius! :D