You can create the new partition in the 40gb space and either:
- Create a new dir in it, and symlink it to your /home,
- Mount the new partition in, say, /home/cirosoto/mountpoint/
To create the new partition, just run the mdk partition tool and create it. Then, format it (if you want win to be able to write to it, format with fat32).
After doing this successfully, mount by the command line first. If you are satisfied with the results, just write the new entry to your fstab.