Using such a hack to change language entails some risk, as outlined here: http://social.microsoft.com/Forums/uk/genuinewindows7/thread/6f6b1cb8-e84e-4c1f-a2ac-181a77d2f772
Your installation of Windows may deactivate if you use such a hack.
If you wish to gain multi-lingual support for Windows without risk, you will need to buy Ultimate or Enterprise.
Depending on what you use your computer for, you may find that Linux Mint can fufil your needs, Linux Mint is free and unrestricted by langauge, but may not run all your WIndows applications (alternatives are avalible). http://www.linuxmint.com/