I has thinking about this thought for the @OP is why not use a download manager to download the avast setup file after like it hits like 10mb downloaded so far.. pause it and resume it later then pause it again at 20mb and so one till it gets done (or something like that).. i wonder if that would help...
When I was on dial-up years ago, I purchased GetRight Download Manager. Since the ISP only allowed a connection for 2 hour intervals ( one could dial right back in, and usually connect ), it was a great help. If the connection got broken for any reason the partial file was saved, and you could resume later with most servers. The server must support resume, and the file on the server cannot change. Now, I use GetRight because some servers limit their download speed per connection, and opening more connections to the same or different servers for the same file can speed the download quite a bit.
At any rate, Free Download Manager has good ratings.
http://www.freedownloadmanager.org/download.htm The full version is 7 MB download, while the Lite version is 3.2 MB. You can bring the Lite up to Full later by downloading the plug-ins from the same site.