This will not be easy to do for newbies or people with no image editing experience. You need some Photoshop or other photo editing understanding and experience to accomplish the desired result. Eventually WM 6.5 Stanard will hopefully start supporting full screen wallpapers and transparent softkeybars or I will write an app the will automatically convert a wallpaper for you but for now...
You will need:
- Your wallpaper that you want to convert (320x240)
- black_softkeybar.png from \Windows on phone running a 3VO ROM (320x26)
- Photoshop or similar photo editing app
Then, copy black_softkeybar.png back to \Windows on the phone and wallpaper.png to \Application Data\Home. To select it, go to Settings, Home, select wallpaper.png as your wallpaper. In order for the softkeybar image to show up, you have to reboot.
Might take some practice but give it a shot...
Here is another pack I threw together for those who want some more ready made ones.