eMachines?
It's just a normal desktop machine? Do you run DOS or
something else? ( DOS may not be able to address huge
disks without tweaking )
If it is you can use basically every harddisk on the market.
( Well, every IDE, for SCSI's you need a controller
somewhere in your machine )
Yes, you could probably do it externally via USB. But that
would mean buying more than just the bare essentials, the
disk. ( if it's USB 1, it's going to be slow )
If you open the computer, that big flat cable leading to your
harddisk, does it have an extra connector on it?
If you have, you can connect your extra (new) drive without
difficulties.
I don't know if "faster" harddisks will pose a problem.
Maybe stick with the 5400RPM ones like you already have.
Though that may be getting tough nowadays.
I'm a bit careful in advising you, you present your computer
like it was put together in the Permian by T-rex hardware
enterprises inc. ( really old
) So just to make sure, ask
in the store before you fork over your money, and ask
what to do if it doesn't work (money back)
Anyway, success
Ojo