What exactly does my T-Cross thing mean?

I have the Sun in House 1/Pisces and Aquarius (I was born on the cusp), opposing the Moon in House 7/Virgo, and both the Sun and Moon are squaring Jupiter in House 4/Taurus.

I've read that this is called a T-Cross. But... what exactly does it mean?

T-cross is a focus

Kyle,

A T-cross in a chart indicates a focusing of energy on the planets/place where the squares occur: So in your chart there is a focus on Taurus (physical) Sun (self-expression) conjunct (energy is combined with) Moon (home, also emotions) focused in the 4th house (home, also emotions). This could indicate strong emotional self-expression.

Explaining,

Tim

What exactly does strong emotional self-expression mean?

And which is more important when interpreting this... the signs the planets are in, or the houses?

Emotional self-expression

Kyle,

"Emotional self-expression" is just what it sounds like: the person with this energy will tend to express themselves emotionally. Perhaps the person will be very passionate about the things they believe in or will express themselves very strongly and emotionally about issues they are interested in.

In interpreting, it helps to use the "astro-sentence" of SIGN modifies PLANET focused on HOUSE. Knowing all three (Sign, Planet, and House) gives the best interpretation of a person's chart. For more about the "astro-sentence" see:
http://www.geocities.com/wilsontctc/

Explaining,

Tim