From Wikipedia:
Through 2009 only taxpayers with MAGI of less than $100,000 in the year of conversion and not married filing separately were allowed to convert from a traditional IRA to a Roth IRA (the converted amount is not included in MAGI). TIPRA 2005 eliminated the MAGI limit and filing status restriction on conversions starting in 2010. Thus regardless of income, contributions can have been made to a traditional IRA in previous years, and then rolled over in 2010 and beyond.

I believe there are additional tax responsibilities you should look into when you make a conversion like this.