1. I hope you attended the purchase of the expansion with your Gamer! This is a big deal in their life, and I am sure they wanted you with them. At least to keep them company in the hours of waiting in line. I went, and it was actually fun. I scored some free loot too (woohoo WOTLK poster)!
2. As they are installing, give them a kiss and tell them to have fun. It's just like sending them off to work (or war, I guess). You may seem invisible for the next few days, so bid them a good long weekend of playing.
3. Nourish them while they are slaving over the computer, leveling their character. Be sure to make them their favorite meals, like nachos with lots of veggies as my hubby requested. Don't forget they also need some good fuel too, so be sure to stock them with some of their favorite fruit that is easy to eat one handed - grapes and apples are good choices.
4. They need fluids! Be sure to bring them large glasses of ice water and Bawls or Rockstar when you see them starting to doze.
5. Remind them to get up and use the bathroom! They won't want to, but it's not good for the body if they don't. If you're a hardcore GamerGirlfriend or GamerWife, you may attempt the South Park bed pan trick. I am not so brave! You could also bring them a bucket for under their desk or suggest they just go out the window.
6. Be patient with them. Soon the hype will be over and your Gamer will be back to his normal self. For now, enjoy some time with your girls!