If your iPhone3G on 4.0 is really slow, chances are you enabled backgrounds in redsn0w. This causes the icons to get a nice shadow, but this shadow processing is just too much for your little old 3g. You can disable the backgrounds by editing a file.

1. SSH to \System\Library\CoreServices\SpringBoard.app and edit the file N82AP.plist
2. Alter the key "homescreen-wallpaper" to enable/disable wallpapers alter this key

key>homescreen-wallpaper /key>
true/> to this:
key>homescreen-wallpaper /key>
false/>

     3. Save the file, respring (maybe reboot).


Install Winterboard !!!!!