In your BIOS:
1) Turn off USB boot.
2) Turn off auto-detect of IDE drives
3) Set the boot order to boot from the HDD first.
In your OS:
1) Turn off any functionality that's unused (network connections, firewall, etc.)
2) Turn off any programs that load at startup that you don't need
And read through this forum to see what others have done... There's a load of information.