This is from a window manufacturing website, but it talks about the tax credit for up to $1500 for replacing windows with more energy efficient windows.  There are other energy efficient updates you can do and get a tax credit for also.  You can google the $1500 energy efficient tax credit and many of them come up.

Here's How the New Federal Energy Tax Credit Program Works1

Section 1121 of the stimulus package allows for a federal energy tax credit to homeowners, up to 30% of the cost of window and door replacement (or, a maximum $1,500 for taxable years 2009 and 2010). The tax credit is for the cost of the product only and does not include the cost of installation. To qualify, windows and doors must have a 0.30 U-factor and 0.30 Solar Heat Gain Coefficient (SHGC) or better. Learn more about federal tax credits for energy efficiency on the ENERGY STAR website(www.EnergyStar.gov).

Additionally:

A local window company, Beyers Windows & Doors Inc. has just given me this information.  Contact Greg King at 303-888-5970

Until June 1, 2009 customers that purchase current Energy Star rated windows and door that would qualify for  the old tax credit can qualify without worrying about the 30/30 rating now. This will be re evaluated at the end of May and I am sure there will be more updates.

 

Energy Star Label Qualifies Some Products For Now

Windows and skylights meeting current Energy Star requirements are currently eligible for energy efficient tax credits established unter the American Recovery and Reinvestment Act, according to an April 22 Internal Revenue Service press release. That eligibility, which would mean these products would not have to have a U-factor of less than .30 and a SHGC of less than .30 to qualify, is scheduled to end June 1, or "until guidance is released."

Headlined "Energy-Saving Steps This Year May Result in Tax Savings Next Year," the IRS relesase says,  "homeowners generally may continue to rely on manufacturers’ certifications that were provided under the old guidance. For exterior windows and skylights, homeowners may continue to rely on Energy Star labels in determining whether property purchased before June 1, 2009, qualifies for the credit." 

Acknowledging the stricter 30/30 requirements for tax credits written into ARRA, the IRS notes, "Homeowners should be aware that the standards in the new law are higher than the standards for the credit that was available in 2007 for products that qualify as 'energy efficient' for purposes of this tax credit. The IRS will issue guidance that will allow manufacturers to certify that their products meet these new standards."

A number of window manufacturers had become aware of the IRS statement and had started notifying customers that Energy Star labeled products would qualify for the tax credit, even if they didn't meet the 30/30 requirements. Window & Door confirmed with knowledgeable sources that such an interpretation is correct, based on what IRS officials are saying now.  Those same sources also offered some caveats.  First, the June 1 date could change once the "official guidance" is released, and second, the interpretation of what products might qualify for the tax credit.