I gave TinyXP Rev 09 a try recently as a guest in VirtualBox. (I do have a legal license for Windows XP, so while that definitely doesn't make downloading TinyXP legal, I feel that morally speaking it's ok).
I wasn't able to browse for shared folders at
\\vboxsvr as I expected. It is, however, possible to map these folders to drives using the "
net use" command:
net use z: \\vboxsvr\david
That worked perfectly. Have fun!