Every version of Windows 7 can use the Japanese (and many other) Input Method Editor (IME). And every version can display Japanese text.
The only thing you need the language packs for is to change the User Interface Language (ie, the language shown on menus, buttons, toolbars, dialog boxes, etc.).
Here is some Japanese text I entered on my Windows 7 system, even though I have no language pack installed:
To activate the Japanese input capability:
Open Control Panel -> Region and Language
Click the "Keyboards and Languages" tab
Click "Change Keyboards..."
Click the "Add..." button to add the Japanese IME.