This tutorial uses named pipes, for com0com serial tutorial look here: viewtopic.php?t=7867
I test this way under Windows Vista x64 and Windows 7 x64 without problems.
You will need:
- VirtualBox (you should have it)
- Putty (link to exe)
- ReactOS ISO (you already know how to get this)
We will use named pipes, because com0com (wiki link) doesn't (or at least didn't) work on 64-bit Windows.
NOTE: name for the pipe used in this tutorial is "ros_pipe", you can use whatever name you wish
STEP1: VirtualBox setup

STEP2: Set up Putty as depicted, set some name under Saved Sessions and press Save, then you can connect using double-click on that name (it's highlighted in blue on the screenshot)

STEP3: Start Virtual machine and install ReactOS as usual
(picture unnecessary)
STEP4: When booting, select "ReactOS (Debug)", otherwise you won't get any debug output!

STEP5: Connect with Putty
(see picture under step 2)
STEP6: Enjoy your debug logs

Some notes:
- Your VM has to be running prior to connecting with Putty
- If you close VirtualBox machine with Putty connected, it will say "Error reading from serial device". That's ok, next time you start your VM just click with your right mouse button on Putty window titlebar and select "Restart session"
- When you select some text in Putty, it will be automatically copied to clipboard
Changes from first posting:
- removed mention about administrator privileges, they are not needed at all
- tiny stylistic improvements
- more tiny stylistic improvements (Feb '13)
