Step 1: Register for free account with IK Multimedia
https://www.ikmultimedia.com/userarea/newuser/index.php?REDIRECT=FREEPRD

Step 2: Download Amplitube 3 (Comes with small selection of pedals and amps)
http://www.ikmultimedia.com/products/amplitube/

Step 3: Download Custom Shop (like the catalog of items for amplitube)
http://www.ikmultimedia.com/products/amplitubecs/

Step 4: Launch Amplitube, log into it

Set 5: Open Custom Shop. Browse items and try for 2 or 3 days I believe for free.

It all works really well.