I recently realized that money I was receiving from a trust was taxable income.

I was an F1 student from Fall 2005 to Spring 2007, an F1 on OPT in July 2007, and an H1 since July 2008. My employer deducts taxes from my paycheck.

What tax files do I file? Last year I filed a 1040NR-EZ and an 8843, even though I was done with my studies in May 2007 and was working by October.

I would imagine I would have to file a K1. But how much do I owe from previous years?

Help?!

I'm a French national.

K-1 page 2 has instructions on how to report the income.
For previous years you may have to file amended tax returns.

If the trust is from France, then the distribution from the trust was NOT taxable for 2007 and earlier, because it was income from OUTSIDE of the U.S. and you, as an international student, was NOT subject to taxes on that money.

That circumstance CHANGED in July of 2008, because you assumed resident status when you converted to the H-1 visa. After the H-1 visa became effective, the trust distributions became taxable income.