To Change Entire Database to support Mutlilanguage

HI,

I have Sql server 2008 database with 200 GB in production.But It will not support multilanguage Since all the tables and procs is having varchar datatype.

I need to change the Entire Tables and procs to support Multilanguage(nvarchar,ntext) .

PLease note I have Many Huge data tables with numerous index .ALso I could not afford too much down Time.How can I perform .PLease advise.