The download manager I have now has an acceleration patch in it :)
It won't benefit dial-up. Segmented downloading is a means of breaking up a file into parts (segments), and requesting each part from a mirror. The idea is that by spreading the load across multiple servers, especially if those servers are busy, the user can achieve faster download speeds: a heavily taxed server may not be able to upload to the full capacity of a broadband connection. However, dial-up users aren't going to strain servers in the same sense. The overall download speed isn't likely to increase unless the server is running exceptionally poorly.
There is another issue: each new connection will have its own overhead. You don't just recieve 250KB, for example, when downloading a file that's listed as that size. The file is broken up into packets, each of which has extra data attached. Moreover, due to the nature of TCP as a reliable transport protocol, there's extra network traffic as the protocol notifies the sender of errors and acknowledges successful receipt.
Mike