Not really sure, I think just hanging out on the internet and browsing forums and stuff. I must have been 12 or 13 or so (this is probably like late 2005). When you're into the bands I was when I was a kid (Rush and Maiden and other classic progressive-ish metal bands), Dream Theater just sort of naturally comes up (what with them being the most popular underground band and all). First album was Images and Words, which I grew to love, though I think it was a bit too heavy and complex for my tastes back then. As a result, I would sort of just end up listening to Surrounded again and again (that one's still in my top 10). Learning to Live and Metropolis just left me confused.
Anyway, while I&W didn't speak to me immediately, I stuck with it and listened to it repeatedly, only because I had a feeling I would eventually get it if I stuck with it for long enough. (My dad had taught me that a lot of really great music can take multiple listens to digest properly.) After Images clicked, it was sort of a free-for-all. SFAM came next, I think, then Awake and 8V and SDOIT. I heard WDADU, TOT, and FII later because, of course, the internet seemed more divided about how good those albums were. Score was the first release while I was a DT fan, though I still only had a vague familiarity with their music.
I got SC on the day of its release (made my parents drive me and all that). I liked it initially. Saw DT for the first time on the Chaos in Motion tour. Met MP and got my copy of Score signed on the day of the show.
I don't know, I think the honeymoon period wore off, because after a while I was really disappointed with SC. As much as I liked the overwhelming majority of DT's back catalog, I was unenthused enough about the band's direction that I didn't buy a physical copy of BCSL and instead just downloaded it from iTunes. Sort of weird, I guess, that I got into this band whose current musical output was so unappealing to me, but DT had cemented itself as one of my favorite bands by the time BCSL rolled around.