If it asks for a 3 letter code, put in what you see (designed to stop automated downloading I think), give it 45 seconds or what ever it says, then there will be a button saying 'click here to download' on the right-click on this and it should give you the option of where to save it and it's all yours!
If you can't see this button, there may be a big advert on top that you can close and reveal it beneath.....
Hope this helps!
did you do everything shoey described? all you need is the grey download button, ignore the ads, also there's a big 'megaupload links' ad box that gets in the way sometimes, click the x button to get rid of it. and remember to wait for the 45 seconds to pass after you've entered the code