What is the difference between T'ai Chi Ch'uan, Tai Chi and Taijiquan?

None. They are different spellings and shortened versions of the same term (taijiquan is the modern pinyin spelling and tai-chi is sometimes seen too)

What does Tai Chi Chuan mean?

It has been translated as 'Supreme Ultimate Martial Art' but I prefer 'Martial Art Using the Principle of Yin and Yang'.

What is the age range in classes?

This varies from class to class but expect a broad range of ages, (teens and 20's up to 80's & 90's) but it is not common for the art to be taught to children as the training is a little slow for their tastes. Some classes are specifically targetted at the over 50's.

Do you have to be fit to start doing Tai Chi?

No, in fact many of the Tai Chi movements can even be adapted to wheelchair users, although some individual attention is required. Do however check with your doctor if you are in any doubt before starting any program of physical exercise. Also let your instructor know of any disability you may have that may restrict your ability to perform certain movements.

Is Tai Chi a health exercise or a martial art?

It is both (although some teachers teach only the health aspects)! Probably 90% of people starting Tai Chi are there purely for their health, but many go on to embrace the complete art. However if all you are interested in is self-defence there are faster ways to achieve this.
Are classes suitable for men and women?

Generally there is a mix of men and women in a class. Women-only classes are a rarity in Tai Chi and it is generally benefical to have a mix of Yin (female) and Yang (male) energy within a class.

What do you wear for Tai Chi?

No special clothing is required. Any clothing in which you can move freely is suitable eg. tracksuit bottoms, T-shirts and gym shoes (no leotards or thongs please ladies !)

I've heard that Tai Chi is an internal martial art?

Taijiquan is one of the three Chinese Internal martial arts (neijia). The other two being Xing I Quan and Ba Gua Zhang. It is a characterised by soft relaxed movements and trained at a slower speed than other martial arts.

What should I expect in a typical Tai Chi class?

Chi Kung (Qigong) which may be stationary or moving meditation Practice of the Tai Chi Form
Pushing Hands (tui shou) - a two person exercise usually taught from intermediate level
You may also see ta lu, and weapons forms in more advanced classes not forgetting warm-ups etc.

Some General Principles

Suspend the head
Hollow the chest and raise the back (but don't overdo it)
Relax the waist and hips
Don't be double-weighted (or indeed double floating)
Sink the shoulders and drop the elbows
Use intensity rather than force
Move as a single unit
The mind and body together
Move like a cat about to pounce
Keep a calm mind