You can download the track up to three times in your choice of formats (MP3, iPod-native MP4 or WMA), and you can download each track up to three times.
ALL PROCEEDS BE GOING TO CHARITY, YE SCURVY SINGLE-BUYERS! Just go do it, it's worth it. This is my first EVER digital music purchase (and it's likely to be my last too, the physical medium is great - vinyl and CDs for the win!) so if I think it's a worthwhile cause, you should too. There's also links to buy from iTunes or Virgin's site, but they'll both have DRM slapped onto their copies (fucking DRM, grr) so both they - and I - recommend the Indiestore route for your purchasing.