S.Z.
Hello - the short answer to your question is that you have three years from the due date of your 2007 return (4/15/08)or the date it was filed, if you filed for an extension and filed later than 4/15, to file an amended return. There may be other things to consider, but this is the basic guideline. Hope this helps.
Just so you know where this is coming from, I am a CPA - have been for 30+ years.
S. Zeiler