People gain and expend their energy in different ways. As you may have heard, introverts get their energy from downtime -- being left alone to read, watch movies, surf the web, daydream, create and otherwise "recharge." They don't have a problem with being alone; in fact, they'll go a little stir crazy if they don't get sufficient alone time. If you think of life energy as equivalent to money, downtime is how introverts make the cash they need to live.
|Not lonely, just recharging.|
This is why introverts, almost to a one, would gnaw off their own legs to avoid small talk; fluffy cotton-candy conversations about the weather and everyone's health and "how 'bout them Mariners" exhaust their limited energy reserves, and offer very little mental sustenance in return. This is also why many introverts avoid parties, especially parties where they don't know anyone; small talk is often the first step to getting to know others better, but introverts have such low tolerance for idle chitchat that they don't end up making new friends at such gatherings. Instead they tend to hover in an obscure corner, just breathing and listening to other people, or they flee the intense mix-and-mingle areas and find a quiet place to take a ten-minute introvert break.
But just because introverts don't like small talk doesn't mean they don't like to talk at all. They just want their conversations to be meaningful. (Remember, they've got a limited energy budget, so they want the most bang for their buck.) Generally speaking, then, introverts are drawn to conversations about ideas -- especially ideas that are already important to them. But they can also be genuinely interested in the ideas that make others tick, especially if such people are unabashedly enthusiastic about their passions. Seeing someone just light up about a concept that makes him or her happy is an experience well worth expending one's limited energy on, at least by my lights.
Introverts are opinionated (sometimes very opinionated, if my own example is any indication), but often won't venture to make comment unless someone asks first. So be the one who asks. Just be prepared for anything; many introverts are philomaths and are full of wide-ranging, interesting tidbits they've soaked up during their downtime. (Oh yeah, and if you want to be a mighty juggernaut at Trivial Pursuit team games, get their contact information! AND LO, YE SHALL BE THE UNSTOPPABLE INFOMANIACS!)
Oh, and another thing: some introverts have a tough time making prolonged eye contact during conversations. This doesn't mean they're not interested in what you have to say. Introverts tend to have an easier time making eye contact when they're relaxed; this tends to happen most often with people they've known for a while, or people whom they trust. Give them time. Meanwhile, take confidence in the knowledge that if an introvert deliberately chooses to continue a conversation with you, he or she is interested -- eye contact or no eye contact.
Some of my friends are introverts, so I'm going to be the one who asks: what's the best way for someone to engage you in conversation without making you want to hyperventilate and retreat to a locked room somewhere?