You can edit XML files using notepad on your PC. The XML files are located in the application data/home folder on your phone. Copy the original to your PC, tinker with it, give it a new name then copy back to your phone so you don't lose the original!
Google how to make wm5 homescreens for more info. That's what I did. I've got my homescreen the way I like but I don't have any info in my notes about how to make the start & contacts buttons transparent...IF it can be done at all. I don't know. For sure the icon bar can be made transparent though. I've seen that.
Devices: T-Mobile MDA (Cingular SIM), i-mate SP5m (sitting in a drawer at the moment while I attempt to migrate to PPC permanently), Cingular 3125 (unlocked and in use on T-Mobile), Motorola MPx220 (retired), Motorola MPx200 (retired)
Accessories: Plantronics Explorer 330 & 2G Patriot Micro-SD (use w/MDA), Kingston 2G mini-SD used in SP5m, Plantronics Discovery 640 & 2G San Disk micro-SD (use w/3125), Jabra A210 BT adapter + Motorola HS805 (retired)