After a lot of googling, I could not find the right way of configuring my VirtualBox for serial com port. After some hit and trail, I have finally got my VirtualBox guest access the serial port and I would like to share my experience with others.
VirtualBox version: 1.5.6
Host OS: Windows XP
Guest OS: Ubuntu Gutsy, 7.10
Machine type: Lenovo T60p laptop (mounted on a docking station)
If your windows com port is com1, configure virtual box as shown in the figure:
Open the windows device manager (can be opened by right click "My Computer" in Explorer->Properties->Hardware tab->Device Manager) and check the configuration for the com port your specified for your guest virtual machine. You will have to set the configuration parameters same as the client that you use in the Linux guest.
I was using minicom in the linux box and faced problem that I was receiving data from the serial input, but was not able to send any commands from the minicom terminal. Then I found that the flow control was enabled in minicom, but was disabled in windows serial configuration (above).
Setting similar properties for both enabled me to use serial port flawlessly