You must already have Snow Leopard installed on your Hackintosh and Fully updated to 10.6.8.

Step 1 : Purchase Mac OS X 10.7 Lion from the Mac App Store for $29.99 and let in download normally or download it from Torrents.

Step 2 : Open it up and click continue, agree to the licence and Then click install on your current snow leopard disk, Don't worry it will not actually install it will just copy some files over. Reboot

Step 3 : Prepare the Installer Partition
1. Boot back into your existing Snow Leopard installation.
2. Open /Applications/Utilities/Disk Utility
3. Highlight your Snow Leopard drive in left column.
4. Choose the Partition tab, and Click the + to Add a Partition.
5. Name the secondary partition Installer with a size of 8GB or 12GB and click Apply.
6. Click Partition.
7. Close Disk Utility

STEP 4 :
1. Download xMove
http://www.tonymacx86.com/downloads
2. Double-Click xMove, and choose Installer as Destination.

WARNING: DO NOT choose existing Snow Leopard as the Destination.

Do not interrupt the process- it will only take a few minutes. When done, you'll have a secondary partition on your drive containing the OS X Lion Installer!

STEP 5: Boot Installer & Install OS X Lion
1. Reboot- at the Chimera boot screen, choose "Installer" as Hard Disk to Boot.
2. It will boot directly to a familiar Mac OS X Installer complete with Disk Utility.
3. Install OS X Lion over existing Snow Leopard or onto any empty drive or partition.

If you've installed directly over an existing Snow Leopard installation, you're done! You should already have done proper post-installation steps on your existing Snow Leopard drive, so skip Step 5 and simply reboot into Lion!

All credits to tonymac http://tonymacx86.blogspot.com/

This will work on:

A System Running Mac OS X Snow Leopard 10.6.6 or later with:
Intel Core 2 or above, 64 bit CPU
Mac App Store Account + $29.99
Internet Access to Download 4GB OS X Lion App through Mac App Store
4GB space available in /Applications
8GB additional free space on your hard drive
Mac Pro 3,1 system definition and the latest Chimera Bootloader from MultiBeast

Check the Video Tutorial for more convenience :