Here is a really good place to start....
http://www.speedguide.net/Cable_modems/cable_patches.shtml
This is a very well informed site for adsl also.
Make sure to download the MS file vtcp.386. I saw a large improvement over my adsl after this patch.
"According to Microsoft, because of a math error, the Windows 9x TCP/IP stack incorrectly computes a timer used to retransmit packets (based on round trip time to a server). When you are transmitting packets over high-speed/high-delay networks, such as any broadband Internet connection, this can result in unnecessary retransmissions and lower throughput... This fix helps reduce retransmission of packets, therefore improving the overall performance of the TCP/IP stack. While It achieves that, in some systems it might also reduce throughput a bit, since it increases the wait before a packet is retransmitted. If you decide to install this fix, backup, or rename Vtcp.386, located in the \Windows\System directory, so you will have a way of going back to your original setting."
SilverBack