Internet Explorer has a file download limit of 4GB (2 GB on IE6). Firefox does not have this problem (haven\'t tested safari yet) (More info here: http://support.microsoft.com/
bittorrent?
There have been a few web-based versions already (bitlet, w3btorrent), and Azureus was built using java, so it's definitely possible.
Edit: @TonyB is it limited to port 80?