I went for an Interview with Rare during the N64 days, that job died in the interview room because they were sure they could match my previous salary (My previous job was a design engineer at Ford. . . They couldn't match it)
I then started work for a few months at Sega in London, testing various games on the dreamcast.
Not a great deal of advice I can give to be honest as Rare would have worked out if they hadn't been so cocky and the Sega job kind of fell into my lap when I called them everyday and badgered them for a job for around 3 weeks.
What I can tell you is the job itself is not all fun and games.
My first day at Sega and they put me on a very early version of Sword of the Beserk, I finished it in that day and hated almost every minute of it.
But the job can be soul destroying, I spent 4 weeks playing the first level of Ecco the Dolphin (which I hated) prior to release, I believe the UK version got delayed for a few days as a result of a bug I found on the final version (That's ok Uk, you're welcome).
But I had some fun there too, I worked on the original Tony Hawk Pro Skater, Chu Chu Rocket, Sega Worldwide Soccor European Edition, Resident Evil Code Veronica and Bust a Move 5 all of which were great to work on and the guys in the office were really cool which meant for a nice work environment, but the problem i found is that I was living with my fianceé and child and could not afford the travel into London on a daily basis on the very low wage that Sega paid, as a result I had to leave the job.
It was fun (mostly) while it lasted though and was a good experience to have.
Best of luck
EDIT:
Interview-wise, Sega didn't have an interview process at that time for it's testers, which was why the phone-them-and-bug-the-crap-out-of-them approach worked.
Rare asked the usual getting to know you crap, fave game, what would you change about it and why? How long do you spend playing? How long have you been a gamer? that sort of stuff, before moving on to specifics about the job and discussing salary.