I have installed wubi on one of my NTFS partions, I chose this one, because it had the most free space, but for some reason wubi does not mount it automatically, can I mount it manually?
I'm a bit confused by your question. Wubi uses a loop file to store the Ubuntu install. You will be able to mount the loop file from Windows as long the filesystem in Ubuntu is ext3, ext4 might be more of a problem.
Please see the following forum post for more info:-
If Wubi cannot access the loop file, it may be because there is a file system error on the NTFS partition which needs to be addressed first.
More info needed.