Unplug all other HD's and peripherals.
Make sure you have the latest BIOS version installed from the emachines Support Downloads webpage for your model. If so, reset the CMOS: Clear CMOS - 3 Ways to Clear the CMOS - Reset BIOS
In BIOS setup, set SATA controller to AHCI first, then IDE mode if that fails.
Wipe the HD with zeroes before trying install. In the tutorial BFK posted just above, partition using Step 2.2 to Format a Primary NTFS partition then mark it Active.
After install, you can plug back in the Vista HD to access it's data or boot it using emachines F10 key at bootup.