Could anyone tell me which free software can use to type Chi

Could anyone tell me which free software can use to type Chinese?
I need to type Chinese,but my PC cannot support insert Chinese.
Please help me.I want to find a free programme which I can use to type Chinese.
Thank you!
please give me exact wedsite.
Mine is Vista system.
I get no cd and I don't want to insert any new system.
Mine system is Chinese
Can anyone help?