This guide will teach you how to jailbreak AND unlock your iPhone 2G running 3.0 firmware using RedSn0w on Windows.
I strongly recommend you backup and restore your iPhone 2G to 3.0 firmware via iTunes BEFORE you begin this guide.
You will need RedSn0w 0.7 which you can download here along with the iPhone 2G 3.0 firmware file available for download here. You also need the 3.9 and 4.6 bootloader files. Download 3.9 here and 4.6 here.
Once you have downloaded everything, extract RedSn0w 0.7 to a location on your computer. You should see redsn0w.exe. Run it.