Savannah22, if you only have dial-up, what I've done for others with only dial-up who want Avast is to use (or ask a friend) if they can download it for you onto a USB stick/flashdrive or other portable device. The download application for Avast 5.0.507 is 47,283 KB. Once you install it onto your machine and get it set up, then you will need to download all the upgrades (that will take quite some time), but at least you will have the program installed and have some protection.
The other option you can do if you have a modem in the home and only your PC has dial-up, is to temporarily hook your PC up to the modem for the download with an Ethernet cable (or WiFi if available and your PC has the capability).
Once Avast is installed and running, go to Settings, in the upper right hand corner of the GUI, go to the left hand panel and set your updates for automatic or manual. I found with the incremental updates on dial-up, that the automatic ones aren't that long.
Since you started the download but it is incomplete, please uninstall Avast so you have a clean install when you do it next time around and you don't encounter problems. I would also suggest that you download the Avast Uninstaller Tool do to a complete clean up.
There are work-arounds that can be done. Let me know how this works for you.