I'm not very sure, but I believe this was asked on the Ubuntu forums, too. As far as I could tell from the responses, this is not quite possible. What you can do, however, is copy your /home/user (where "user" is your username) to your Windows partition and install a fresh Ubuntu alongside Windows. Then copy the contents back from the Windows partition and you'll have an Ubuntu install that is almost identical to your wubi install. The only things you will notice that are lacking are the programs you had installed. You can re-install these and they will have exactly the same configuration as before.