Older windows are often big energy wasters. Buying new, energy-efficient windows is one way to reduce this lost energy, but there are also several inexpensive repairs that can improve the performance of your current windows.
Any drafts you feel when standing next to a window are likely due to air infiltration around the window frame or sash perimeter. Address drafts by installing sash locks and weatherstripping around the perimeter of the window. For double-hung windows, consider side-mounted sash locks that pull the window tight to the sides of the frame, not just where the sash rails meet.
You also can remove the inside trim surrounding the window to see how it was installed into the framing cavity. Any air space between the house shell and the window frame can cause significant air leakage and should be sealed. If the gap is not too wide, then it can be sealed with caulk, backer rod or nonexpanding foam. For windows with ropes and pulleys, buy pulley seals to stop air infiltration there.
You can reduce heat loss through windows by covering them with plastic window film or insulating window inserts, such as those available at Windo-Therm. Another option is to make simple window quilts by sandwiching a piece of Bubble Wrap between two pieces of cloth material, which can be rolled up and down as needed.