http://www.techspot.com/tweaks/winxp_modem/index.shtml
Internet Connection Setup
Click on Start, Control Panel, then Network Connections. Right click on your Internet connection & select Properties. Then select Configure button.
Maximum speed (bps). Users of 33.6K Modems should set this to 56700, while 56K Modem users should select 115200 .
Enable software compression
Those with Winmodems should Tick this for optimal upload/download speeds, albeit it at the cost of some CPU cycles.
Default below is Unticked .
Negotiate multi-link for single link connections. You can leave this setting Tick unless you experience problems connecting to your ISP (Error code 733 according to Microsoft), in which case Untick this.
Start > Connect To > ISP > Properties > General > Configure .
Enable modem compression
Should you have a Winmodem then you can leave this setting Unticked as these Modems do not support hardware compression.