You typically set the baud rate to match the connected device. It probably goes up at least to 115200. Dialup modems are typically 57600, and serial printers (if they still exist) may only be 9600. This setting is either done in the Properties for the device, or (more usually) in the software application that is using it.
Under Windows XP go to :
Start -> Control Panel -> System -> Device Manager
Expand Ports (LPT & COM)
Right click on Communications Port (COMx) and select Properties
Select the "Port Settings" tab ...
You can select the bitrate here (sorry for the step by step like guide).