Even if your modem is working well, the baud rate of your COM port might not allow you to reach top-speeds. To improve the port's speed:
1. Click Start > Settings > Control Panel >System
2. Under the Device Manager tab, click the '+' sign next to Ports (COM & LPT).
3. Select the port your modem uses (usually COM2), click Properties, and on the Port Settings tab set the Bits per second to 115200 bps.