Use Startmount to auto-mount harddrive and other media's partitions on boot up.

It will scan which drives available for mounting and to let you choose which one(s) or all, to automount at next boot.

It can also auto-run a chosen program(s)

So, boot, it will mount drive and launch a program, if chosen.

The program can be accessed via PupControl-

PupControl > Drives > Startmount

Or via the terminal command /usr/local/Startmount/Startmount

You'll may want to disable the startup splash, select File > Preferences from the main window.

Puppy is built into Puppy 5.2x Lucid and some other Puppies. Select from menu or PupControl.

If its not built-in, like on Puppy 5.3 Slacko, you can download and install the PET from the Startmount thread.