When I worked in that industry, I was always coming across people who were complaining about cold rooms and internal condensation.
The best way to reduce condensation is to increase ventilation. However, most people then complain that it makes the room colder and increases their heating bill.
The thing is, seal a room and heat it and it generally increases humidity and thermal currents: Hot air will be drawn to a cold point in the room (often a window) and the moisture in the air will condense on the glass and cause condensation. It will also draw cold air into a warm space and make it feel draughty.
Low E glass typically has an insulative coating on surface three of a double-glazing unit and this tends to increase the surface temperature of the inside pane. The result is that the window is no longer the coldest surface in the room and the moisture in the air then condenses somewhere else - often a cold wall. This is less noticeable because the surface area of the wall is greater than that of the window - but it still happens.
Filling the glazing void with a denser gas improves the insulative properties of the glazing unit. Argon is a typical example. At one time glazing salesmen sold units on the gap between the panes - 20mm being typical. The last time I looked, the optimum gap for air was considered to be 16mm. With something like an argon fill, a like for like or better performance could be achieved with a 12mm gap. Generally, in replacing glazing units in existing frames you are stuck with the existing stack height - it being very difficult to retrofit thicker beads (in uPVC at least) to compensate for thinner and more efficient units.
Triple glazing, fine in theory and I've had it. I wouldn't have it again, here's why: every double-glazing unit has a working lifetime. Largely a function of sunlight, over time, the seals between the units break down. Once there is an avenue for air to travel from outside the unit to between the panes the glazing unit starts to act like a bellows. Moist air can travel across the gap and the moisture can condense inside. Over time, this leads to misting between the panes. With double glazing you have one set of seals. With triple glazing you have two (so twice the risk). Also with triple glazing, you have a 50% heavier unit, and many installers do a poor job of installing heavy units. If each pane in the glazing unit isn't properly supported when it is packed into place a pane can slip and this causes the seal to prematurely fail. Our previous house was terrible for this - all, luckily replaced under warranty and watched by me during replacement!
In the case of the original poster, firstly, make sure the room is properly ventilated. If the units still condense, then consider replacing them with Low emissivity glass (Low-E). It can be a relatively cheap thing to do and plenty of companies can do it for you. Don't bother to insulate the frames - most have some form of honeycombing which does a passable insulation job and, anyway, the surface area of the frame is small compared to the glass.
