iPhone developer iH8sn0w has just pushed yet another update to Sn0wbreeze, bringing the version number up to 2.2.1. This new release fixes issues when jailbreaking Verizon iPhone 4 on iOS 4.2.6, adds drag and drop IPSW files support, 100% fixes the iBooks issue, and all the issues that you maybe experiencing when using Windows classic theme.
sn0wbreeze 2.2.1 now at http://ih8sn0w.com (Fixes Verizon iPhones, iBooks 100%, Drag & Drop IPSW implemented, and Windows Classic issues).
oh, and it also fixes iREB issues for the iPhone 3G on "Waiting for iBSS" for some machines.
Once you are done with the jailbreak, you can unlock your iPhone 4, 3GS and 3G on the old baseband using Ultrasn0w 1.2.
Mac users can follow our PwnageTool 4.2 step by step guide posted here.