Heres the command::
ipsw OrigFirm/iPhone1,1_2.0_5A347_Restore.ipsw CustomFirm/custom.ipsw -e "Phone Activation" bundles/Cydia.tar
ipsw:: ipsw is the exe file that doesa the work. If you just type "c:> ipsw" and press return you will see all the options it takes.
OrigFirm/iPhone1,1_2.0_5A347_Restore.ipsw:: This tells ipsw to look in the OrigFirm folder for the iphones ORIGINAL firmware, which you downloaded. iPhone1,1_2... is for 2g phones and iPhone1,2_2... is for 3g phones.
CustomFirm/custom.ipsw:: This tells ipsw to save your custom firmware in the CustomFirm folder. You can change the name of your custom firmware. This is a good idea if you make different ones with different logos, packages etc.
-e "Phone Activation":: The -e command tells ipsw NOT to do something, in this case NOT to activate the phone because we are on a legit iPhone carrier contract.
bundles/Cydia.tar:: You can add packages to xpwn which get built in to the custom firmware you are making. The most common is Cydia, the new iPhone installer for homebrew software. They live in the bundles folder.
Running this command will build a custom firmware that will unlock your 2g phone but not activate it.
If you want to add boot and restore logos you can! Just change the command slightly::
Add -b Logos/boot.png -r Logos/restore.png
ipsw OrigFirm/iPhone1,2_2.0_5A347_Restore.ipsw CustomFirm/custom.ipsw -b Logos/boot.png -r Logos/restore.png -e "Phone Activation" bundles/Cydia.tar