I'd also check with replacement window people and ask if you can have the old windows they are removing from jobs. They have seemed thrilled to have the old stuff picked up at the work site as long as I wasn't taking them for resale.

In ithaca, Ny there is a place that collects old stuff like windows, doors etc.
http://www.significantelements.org/significant_elem.htm

Here is a link that might be useful: Significant Elements

Here in MA all windows installed have to meet energy star qualifications, dont know if its the same in CT but if you are going to have building inspectors around I'd hate to see you waste money on installing old windows you cant use.

The Habitat For Humanity ReUse stores have lots and lots of replacement windows. And other house parts you might like!

http://www.ihateticks.com/friends.html link in the lower right corner of page

Here is a link that might be useful: habitat re-use stores

There is no energy code problem with using old windows MA although I would advise against it since the likehood of earlier insulating glass seal failure is so great. It's not a good investment.

The residential energy code for Massachusetts is contained in Appendex J of the Building Code which contains no mention of the Energy Star program which is a voluntary energy conservation program sponsered by the EPA.

In MA the windows of a house have no minimum standard; they are considered one element contributing to the total heat loss of the structure. The easiest way to show compliance is to enter heat loss and equipment efficiency information for the entire structure into a computer program called "REScheck" (supplied by the state) which returns a pass or fail notice. Another way to prove compliance is to have an engineer calculate the heat loss of the structure and certify compliance. Compliance proof must be submitted with the application for a building permit.

There is an exception clause for additions to existing houses which sets the acceptable U & R values for each element of the addition rather than requiring analysis of the entire house. The maximum U-value for fenestration in an addition is .39

The current residential energy code in CT is the 2003 International Energy Conservation Code (IECC) published by the ICC. "REScheck" software can be used to show compliance just like in MA.

Here is a link that might be useful: MA residential energy code

State Energy Code Information
Some states such as Massachusetts have enacted more stringent Energy Code guidelines that require the use of special glazing such as Low-E glass in replacement windows. Please refer to the state building codes for specific guidelines.

Massachusetts Energy Code
The Massachusetts Energy Code states that all replacement windows shall have a maximum U-Factor of 0.44 as of January 1, 1999. All windows must be NFRC (National Fenestration Rating Council) certified and labeled as such.

January 5, 1999 Amendments

Exception 1: Criteria for NFRC listing/labeling and maximum U-0.44 are not required if the existing window(s) are true divided light (i.e. single thickness multi-pane sashes with structural muntin bars) and being replaced with "like kind" units. This exception additionally requires that a storm window be installed over the replacement window.

Exception 2: Criteria for NFRC listing/labeling and maximum U-0.44 are not required for basement windows with a unit height up to 24", whether or not the basement is a conditioned space.

I thought this was a conversion of a porch into a conditioned space which should have to meet the energy conservation code for new construction & additions in CT.

If you can claim you are only replacing windows in existing openings in an already conditioned space, you might be able to use single-pane glass with a "storm panel" like the Marvin windows you have already mentioned and not have to meet any other energy code requirements. That would satisfy building code section 3407 for alteration of existing buildings in Massachusetts but I don't know if that would be true in CT.

For very authentic historic all wood windows with single glazing and "storm panels" on the outside of each sash (U-value .41) similar to the Marvin design, for much less money, try Boston Sash and Millwork in North Dighton, MA (just east of Providence). It's a small old-fashioned window manufacturer that only sells through lumberyards and window wholesalers. They make the white PVC compression pulley type balance system. They also make a "concealed balance" window that has the balance system in the edge of the sash so there is no balance system showing at the jamb, only wood. That feature can be expensive but it looks as good as most custom historic windows.

Marvin also offers an energy panel on the inside of the sash for historic restorations.

Here is a link that might be useful: Boston Sash & Millwork