Eventually I got that key and enjoyed many, many hours of online play with a good friend. I never did get to play the expansion, although I'm well aware it's considered the definitive experience.
Counter-Strike is similarly something else I had to miss out on, I just didn't have a way to purchase games digitally. Steam was around as well as services like Direct2Drive but my Mom didn't have a bank account, so I just accepted that I'd be missing out on these multiplayer experiences as a teenager.
I did manage to keep up my subscription to The Realm for a long time, but that was thanks to the wonderful concept of money in birthday cards. Once WoW launched it basically killed The Realm anyway, I could have spent that money more wisely in retrospect.
Starcraft was a rare multiplayer exception for me, along with Jedi Academy, and UT. It'll always have a place in my heart because of that.
Later in life, I ended up putting over 800 hours into CS:GO and now own over 300 games on Steam, so I lived my multiplayer dreams eventually.
I've shelled out enough for Hearthstone packs by now that I don't feel guilty about trading that now worthless huge chunk of The Realm Online gold for that valuable Starcraft CD key.