Fileshack goodness: http://www.fileshack.com/browse.x?cat=259
(free registration required)
If you have broadband, I recommend getting it from Fileshack, even though they only offer the 1.00 - 1.11 patch (it won't break your 1.03 version or anything).
Then there's 3D Downloads, which is often full and thus giving you 404 errors: http://www.3ddownloads.com/?director.../sin/official/
I guess you should stay away from it unless you're on 56k and need to download the 1.01 - 1.11 patch instead because of file size considerations.