Apparently hooking on to a host OS com port with virtualbox only works if you actually have com ports. So somebody has come up with a solution.
What you need:
1) VirtualBOX
2) Guest OS what wants serial port access for some reason (perhaps serial console)
3) A windows named pipe to TCP proxy program
4) Something that can connect to a TCP port (putty or a telnet client)
And in the manual to virtualbox there is a mention to one, however a user called 'shvechkov' has created a windows program to create this named pipe to TCP socket proxy, you can find the instructions and download at:
Windows named pipe to TCP port made easy (local copy).
An example:
In VirtualBOX:
a) map COM1 to 'Host pipe' and checkmark 'Create pipe'
b) Name the pipe like '\\.\pipe\com1' (the com1 part is your own unique chosen name for the pipe)
In nptp:
a) Create an entry for the previously mentioned pipe and map it to a TCP port (like 700)
Connect telnet or putty (in telnet mode) to localhost port 700 (the port chosen) (unless you have allowed external ip)
That's it, you should have output from the serial port on the telnet connection.