Some of the Mitek cases will hold 2 travelstars....just depends on the case. But I prefer external anyway, because I have the option of plug or power, and the drive isn't always powered up when I'm on batts.
All of the IBM Laptops I’ve ever owned have supported 2 hard drives. IBM has an "Ultra Bay" so you can pop out the CD/DVD drive and pop in a 2nd hard drive, or Zip drive, or floppy drive, or Super drive, or what ever. I've always had 2 HDD's on my laptops.
To be honest, I've never looked to see what kind of battery it takes. I DO know that without power I can only go about 2 hours.
I've been very happy with it. It feels more solid than my wife's HP and another great feature is a numeric keypad built into it (no more using jkl and getting numbers instead).