Heads Up! The American Recovery and Reinvestment Act of 2009 allows tax credits for energy efficient home improvements. The offer for credits began on January 1, 2009 and runs for two years.
The new rules give you through December 31, 2010 to qualify. The maximum credit is now equal to 30% of the first $5,000 spent on high-efficiency improvements. I found more info on this at www.energy.gov/taxbreaks.htm.
Four years ago, Congress passed the Energy Tax Incentives Act of 2005 for purchases made in 2006 and 2007. The good news is that even if you took advantage of tax credits then, you are probably able to benefit again. I believe this is certainly worth a look.