“My house is old and drafty and I need to replace my windows.  I want to stop paying more for heat and energy and need to do something before winter hits.  I consider myself handy.  Is this a DIY project or do I need to hire a windows installer?” says Michael in Colorado

Windows… this is a topic near and dear to my heart.

Unless someone has the requisite skill – I do not suggest installing windows on your own because a great window with a subpar installation is worthless.  In fact it could cause water damage to the house that may not manifest itself for years and might leak air to the point of making the window purchase worthless.   I recommend hiring a contractor you have confidence in that is skilled in window installation or hiring a window installation company.  
If your home has uniquely shaped windows or the frames may be out of square and/or plumb (you did mention that the house was old), you will want to make sure that you have expert installers. And make sure windows are energy star rated by the US govt.  In order to meet Energy Star requirements windows must have a u-value of .30 or less. 

There are so many variables to consider. Is that a full frame or pocket style installation? Is that a vinyl window, composite window, fiberglass window, solid wood window or wood window clad in aluminum on the exterior?  (See below for a list of some of the more common types of windows.)

Buying your windows from installers could also help because many installers have contracted with window manufacturers and the installers might receive and pass along to you better pricing on some window models.  Be advised that there are many types of windows (see below for a quick listing of some more common types.)

Thanks for your question, Michael.  Good luck getting those new energy saving windows in soon.  If you have any other questions, don't hesitate to Ask The Contractor.  
Bruce

For those who visit EERE’s Energy Savers Window Installation page, I will again caution that window replacement is a job that requires a higher level skill and if the job is not done well, will come back to haunt you.
(http://www.energysavers.gov/your_home/windows_doors_skylights/index.cfm/mytopic=13470)

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Here is a quick guide to the many types of windows.

The most common window styles are the Double-Hung and Casement:

• Double-Hung – These windows are basically stacked on top of each other and open by sliding in front of or behind each other. This is a very standard design.
• Casement – Another cranking window; this time it comes from a side.

Other window styles include:

• Awning – An awning window resembles a store or deck awning in that it cranks open from the bottom.
• Bay – A bay protrudes out from the wall plane. A compass or radial bay is very similar and called a bow, and is noted by smoother angles than the bay.
• Fixed – These windows are designed to stay in place and never open.
• Hoppers – These windows are very similar to awnings, but they swing open from the top.
• Jalousie – Jalousie windows are a series of louvers that overlap one another. These windows are very popular in the south as they allow for great ventilation, but not so good in the north because they’re just not airtight enough.
• Oriel – Oriel windows are much like bays and bows, but they’re supported by brackets or cantilevers and are usually much smaller. A very small oriel placed higher up is sometimes referred to as a garden window.
• Palladian –Palladians are a pair of double-hung windows on either side of a single double-hung that has a semicircular window above it.
• Rotating – Rotating windows have a center pivot and can open from either side or top and bottom. These windows aren’t very popular because they don’t easily allow for screens when in the open position, but they’re very easy to clean and a reflective coating can be applied to manipulate the sun’s heat.
• Single-Hung – Much like their brother, the double-hung, these windows open by sliding up and down, but these feature a fixed top half.
• Sliding – Sliding windows slide from side to side to open.
• Windowscapes – To take advantage of a view, windowscapes are entire walls made of windows.