[ubuntu] Accessing Ubuntu from another Ubuntu

Hi All,

I have the following setting: the HDD is split in two, first half is Windows 7, second half is Ubuntu (let's call it U1). In Windows I'm running a VirtualBox in which I have installed another Ubuntu - U2.

Problem: I'd like to mount U1's main partition in U2, but I can't seem to find it. It looks like U2 cannot see beyond himself and host. How can I go around this?

Thanks for your advice,
SxN