Setup COM port in VirtualBox (Host: XUbuntu, Guest: Windows XP)

In VirtualBox Setting,
Port Number: COM1
IRQ: 4
I/O Port: 0x3F8
Port Mode: Host Device
Port/File Path: /dev/ttyS0

If encounter read/write permission error,
add the current Linux account to:
'dialout' Group

In xubuntu, System Administrator > 'Edit Group...' , add current user to the 'dialup' group

Check serial port in Linux:
dmesg | grep tty
If the screen shows out ttyS0, it means COM1

FYI,
as previous 'dialout' group account stated,
ls -l /dev/ttyS0 can view the COM1 permission group.