So I open my eyes wide and finally found something that is really capable of doing what I want to. It is still from Microsoft though. Well the toolkit name is Windows System Image Manager which is part of the Microsoft AIK.
Once you open that up, you are to load an image (just use install.wim in Windows 7 DVD) or a catalog file in the installation source.
After loading up an image or clg file at the left pane, then what you see is a total list of features / settings that you can customize and put into unattended file. Taken the screenshot as an example, the International-Core is related to regional settings in the Windows. So if you want to customize it, just right-click on that item and Add to of the passes in the middle. Each pass is just like a stage in the unattended installation and you don't have to know too much about pass to finish editing your own unattended file!
After you place the feature /setting component in the answer file passes, you need to give proper values accordingly and repeat the steps as needed. My below screenshot showed that I only have one customized setting which is regional setting that was set to be en-au.
Right click on Untitled in the middle pane, you'll be able to save the work and start using the unattended files.
