I'm not sure about this, so don't go exactly by what I say.
But, he probably left it in so you could have all of your data still..
someone correct me if I'm wrong, but can't you have like a partial C Drive on the second hard drive? Like if the 60gig gets full, then it'll just go onto the 300gig? Once again I'm not entirely sure.
About the cache, you will have no problem with the drive being a 8mb. Those are still very good hard drives, so don't worry about the cache.
Although be sure it's a 7200 Rpm, that may affect loading times and such.
I think you should keep the old drive in, no reason to take it out. It's an extra 60gigs..