Of course you can file separately for tax year 2008. Your IRS Form1040 will allow you to be married and file separately. You usually lose some of your tax advantages by doing this, but this option remains open to the both of you.
Let's just hope you won't have to be separated very long. It's better to worry about the quality of our personal relationships than to worry about the IRS. They have lots of money and their relationships are not nearly as friendly as a good marriage.
Good Luck in Maryland!
I might be mistaken, but your real question might be can you filed married-jointly? If that is your question, you should be able to file married-filing-joint as well as married-filing-separate. If you and your husband are "married" according to your "marriage" state of residence (in your example, it would be Colorado), you and your husband can file jointly for your federal return. You would then have to file a separate state tax return in Maryland, and he the same in Colorado. Just because you are living abroad for a year, doesn't mean that you and your husband are no longer married. Thus, you are not precluded from filing married-filing-joint or married-filing-separate.