I tried that and got 'command not found', but have now added vboxmgr to my (windoz7) path (which is exported to cygwin in bashrc).
On windoz7 it lists the vbox name under my cygwin home, where I did the init. It comes up OK and says 'Machine already provisioned.'. When I exec 'ruby -v' it has the new ruby so that setup seems to work OK.
The XP setup is the problem then. I'll have to add VBoxManager to its path and see on that.
On XP, there's a VBox VM dir under cygwin home with the VM I installed pkgs in, and under 'c:\docs and settings\username\VBox VMs' I see new ones get created there when I run 'vagrant up', though I didn't 'init' a vbox there. Maybe the system is confused on the 'owner/user', with cygwin not really doing things the windoz way. Maybe I should just cd into the windoz user dir, init a vbox there, install pkgs and work from there instead of cygwin home.
I actually saved all the commands to install all the stuff I added so am able to go through it again, as I have once already. I intend on putting them into a script called by vagrant during provisioning so I can recreate this sort of setup, but I also need to be able to reuse a setup, like when I start adding data into psql.