can i efile past returns now? like for 2003 -2005?

Answer 1

No only the 2006 return can be efiled, you must submit the 2003-2005 by completing a paper return for each year and mailing it in. You have until April 15th 2007 to claim any refund for the 2003 return, if the 2003 is submitted after that date you will lose any refund you had coming.
Here is the link to prior year forms and instructions

http://www.irs.gov/formspubs/article/0,,id=98339,00.html

Answer 2

Only the current year can be e-filed. You can get forms for previous years on the IRS web site, www.irs.gov, if you need to file.