Try:

s#(?:\bimg\b[^<>]*src|\blink\b[^<>]*href)\=\"(.*?)\"#...

and

s#(?:\ba\b[^<>]*href)\=\"(.*?)\"#
[download]

(diotalevi's solution may be a better place to start, adjusting the .+ to not allow intervening tags.)

Or you may want to follow this suggestion; I had assumed you wanted to cover even something like <a title="whoohoo" href=...>, so I didn't switch to \s*.

But given that you want to be able to handle *any* web page that is entered, you ought to use a real html parser instead. (BTW, I tried http://google.com and was disappointed that the buttons didn't get translated.)