Hi. H&R Block have prepared our tax return for 2007 but believe we should file as married filing separatly as we are non-residents because we are on an L Visa - My husband is on an L1 and I am on L2.
We entered the country on 18th Sept 2006 and left on 4th Jan 2007. We both worked for the full 2007 tax year in the US.
Please can you advise how we should file? Thanks!

I assume you meant that you left on Jan 4, 2008 (not 2007).

For 2006 you should have filed as non-residents (and you cannot file a joint return).

For 2007, you should have filed as residents and filed a 1040 (you can file a joint return for that year).