Rob 1

For the time being, you only want one hard drive plugged in.
For one thing, windows doesn't like seeing two drives during installation and you could wind up with the wrong drive letter associated to the C drive.

So plug the 10gb drive in by itself on the connector that was previously connected to a hard drive, and give it a go.

Note, if you've managed to unplug too much and don't remember which is which, you will need to look at the motherboard connectors. Find the one that says IDE 1, or Primary IDE.
That's the one that goes to the hard drive. The other one goes to the optical drive.

I hope that helps.