Creating a Modified Keymap and Submitting it to the Ubuntu Project
It's great that you are thinking about helping other users of your computer. Here are some steps you can take.
I'll try to give you an outline of the steps needed. The details will depend upon what your computer needs.
Creating a Modified Keymap
The detailed directions for defining a custom keyboard for Ubuntu are here. I would suggest copying your existing keyboard file to a new name and then modifying that file to add and modify what is needed. You can do this with gksudo gedit /usr/share/X11/xkb/symbols/old-name, and make the changes in your editor. Then save them under a new name.
If you forget you can reinstall the xkb-data package.
Activating and Testing the Modified Keymap
Go to System Settings and Select the Keyboard control panel. At the bottom select Layout Settings. Then you can click on the + icon on the lower left to add your new file to the menu, select it, and test it.
Contributing to Ubuntu
If you don't have one, you should get a Launchpad account. Go to launchpad and click at the top right corner to create one. Otherwise please log in.
The next step is to go here and make sure someone hasn't already filed a report. Assuming that's not the case, report the problem that the default keyboard is not adequate for the Lenovo z570 and mention why.
Please attach the file you have created to the bug.
I'd suggest coming back here and providing the link to the bug report. That way others who recognize your question here as their problem can go to the bug report and click on the link that says that the bug affects them.
Helping Even More People
You can go farther than this by checking out this link to the launchpad page for the upstream of this package. Clicking on the Bugs tag shows problems in the upstream package Launchpad knows about. It also shows that Freedesktop keeps a bug reporting system for upstream.
Most distributions of Linux probably use this upstream package, so your contribution can go farther once it has been contributed there. Ubuntu doesn't just serve as a way to help its own users, it contributes back to upstream developers such as those at Debian and Freedesktop to help non-Ubuntu users.
You can click on the link Bugs are tracked in freedesktop.org Bugzilla. at the top to go to the Freedesktop bug reporting system and send them your bug report and new keymap file. Once you do that you should go back to your Launchpad bug report and add that the bug affects the upstream package and put a link to your upstream bug report there. That way Ubuntu developers will know that they don't have to do this themselves.
I can see that the Ubuntu X team is busy at work preparing Quantal, so this is probably a good time to make a contribution. Their mailing list is at firstname.lastname@example.org and I'm sure they hang out on IRC as well.