Broadband ADSL (asymmetric digital subscriber line) typically offers downstream throughputs of 256kbps to 1Mbps and upstream of 60kbps to 256kbps.
ISDN (Integrated Services Digital Network) typically has a varied speed depending on the provider. But one can pretty much guarantee that they'll be at least 5 times as fast as a standard dial-up connection today. However, ISDN is very hard to find since DSL has kind of taken over.
Your connection speed is entirely up to how far your provider is from:
1. your residence
2. The internet backbone
There are a few things you can do to speed it up. If you use Microsoft, your transmission speed is maximised for Modem transmission. Therefore you're not maximized for packet size and transmission speed. This is usually done with registry edits...however, you can find nifty little programs out there that will do it for you. I've listed a few below:
http://www.speedguide.net/downloads.php
http://www.softpedia.com/public/cat/12/4/12-4-41.shtml
http://www.ascentive.com/products/webROCKET.html
Hope everything works out for you and I hope I've answered your questions :)
TKS