My wife and I signed a separation agreement back in May 2008. And we been living a apart since then. Will I be running to a problems if I filled for divorce this year after a year of separation and filed for taxes jointly.
I think that normally the rule is that you must be married at least 1/2 the year to file married regardless of whether or not you file joint or separate.
If you have not legally divorced, you must file married and either jointly or separate. If you obtain a legal divorce this year, you will make that determination for your 2009 taxes based on the date that you are divorce.
You may file your taxes jointly in 2008. Since you separated in May of 2008 you will not be eligible to file for divorce until May of this year. Though you were living separate and apart for the majority of the year you are still legally married an may file as such.