How do I reinstall OS X Lion after having reset the hard drive?

That machine did not come with Lion (10.7). It came with Tiger (10.4). If you are missing the original installation discs, you'll need either either the 10.5 retail, or 10.6 retail installer disc just to get to 10.6, and then apply the 10.6.6 combo update, if you didn't first install 10.7 on the hard drive to begin with. If you did install 10.7 and are having issues, you may need some settings reset by the Mac App Store support or AppleCare:

http://www.apple.com/support/mac/app-store/contact.html?form=account&topic=MacAp pStoreAccountandBilling

Contact Apple for support and service

Note, some Macs may have the Internet Restore with command-R enabled that did not come with Lion, if they use this firmware installation;

Computers that can be upgraded to use OS X Internet Recovery

If you didn't repartition the hard drive in your "reset" to factory settings, the restore installer should be able to install the operating system that was last installed on it. Otherwise you'll have to reinstall 10.7 or use the firmware to enable to restore partition.

i have the same error like "The Falsifier", that's why i can't proceed with this re-install process.

i'm doing this because my System Preference is always displaying 32-bit on the menu bar & going through the get info of the app don't not show the checkbox "Open in 32-bit".

The Falsifier wrote:

I have reset the my mid-2007 MacBook to the original factory settings and am now trying to reinstall OS X Lion that came with it. I was under the impression that I could reinstall it without a disc. I clicked on the hard drive I wanted Lion to be installed onto and typed in my Apple ID and password for the App Store as part of the installation process. I then received an error message stating "This item is temporarily unavailable. Try again later." I restarted the computer and attempted the process several more times and received the same error message. What do I do?

As a brody correctly stated, your MacBook2,1 shipped with OS X Tiger. If you need to replace your Tiger installation DVDs, these can often be purchased from ifixit.com. Having the original installation discs is always a good idea, as the hardware test for a system is only found on the original shipping version. In other words, install discs for Leopard or Snow Leopard will not enable you to run system diagnostics on your MacBook.

To be able to correctly install Lion on your MacBook2,1, you'll need to download the installer from the App Store again (found in your purchases history) from a different Mac. Then you can use DiskMaker X to create a bootable USB stick or DVD. (USB is much faster.)