I used these instructions. Although you run Quick Pwn near the end, it doesn't actually jailbreak your phone - it just makes it 'bootable' again. You only complete the first step in Quick Pwn. Good luck!
Restore iphone from 3.0 to 2.2.1
Put your iPhone in DFU mode
1. Open Up iTunes
2. Have Your iPhone Connected To Your Pc
3. Hold Down The Power/Sleep Button And The Home Button For Exactly 10 Seconds.
4. Then Release The Power/Sleep Button And Continue To Hold The Home Button Until iTunes Brings Up A Message Saying Your iPhone Is In DFU Mode.
5. Click Ok Or Whatever It Is So That It Closes That Popup.
6. Hold Shift Then Click Restore.
7.Then Make sure You Have Downloaded the ISPW Firmware Called: iPhone1,2_2.2_5G77_Restore. (MAKE SURE ITS iPhone1,2_2.2_5G77_Restore AND NOT iPhone1,1_2.2_5G77_Restore CAUSE THAT FOR THE 2G IPHONE).
8. Let It Restore Once Its Finished You Will Get An Error Thats Normal It Will Most Likely Be 1015 Or Something Like That.
9. Download Quick Pwn 2.2.1.
*These steps are very important!
10. Then Open Up Quick Pwn With You iPhone Connected To Your PC And It will then Say That You Need To Hold The Power/Sleep Button And The Home button For Exactly 15 Seconds Then Release The Power/Sleep Button And Continue To Hold The Home Button For 2 Seconds. This will boot your iPhone To the Emergency Call screen.
11.Open up iTunes And Let It Activate Your iPhone.
12. Then Restore your iPhone From A Previous Backup If you Have One.
Edit: loads of places to get 2.2.1 from if you need it such as
http://www.blogsdna.com/2264/iphone-firmware-221-and-ipod-touch-firmware-221-released.htm