Hi, I am an Indian citizen, here (Georgia) on an F-1 visa from Fall 2006. I filed 1040NR-EZ for 2006 returns but this time I have used turbo tax and filed a 1040 last week. I just realized my mistake. What should I do now? Should I file 1040X along with 1040NR to the Georgia IRS center right away or do it after April 15th? I also found that the amount I claimed as a refund on 1040 is more than what I should get by 1040NR.

If you owe tax on 1040NR, then you should file before April 15, 2008 and pay the tax due. Else you will be charged interest and penalty on tax due.

Your deductions on 1040NR and 1040 are same--- standard deduction of $5,350 and exemption of $3,400. So normally tax wise it won't make difference if you file 1040 or 1040NR. But since you are exempt, don't pay FICA taxes you must file 1040NR with Form 8843.
Read: Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents