Hello there and welcome to EP! ^^ I'll try to give you a few hints on how to achieve your goal.

1. You must know how to make icons (just like schmilk) this is the only tutorial I read ever.  This is why you don't find tutorials on things you want to know. Because there is none on how to make a theme to look like applecorp. Your best BET is get on 3.90 and make the icons as "PNG" this is the easiest process because all you have to do is resize what you want and save it as png then just input the icon using rcoeditor. SIMPLE very SIMPLE.  Before it was a bit harder because you couldn't pass 256 colors PLUS you had make alpha channel which is the transparency of the icon.
TIP: Saving as PNG takes more space, if you save them as BMP > Indexed choosing 256colors and back to RGB (photoshop) the icon will look just as PNG and will take less space. But just save them as PNG.. ^^

2. You must know what the "RCO" files contain as well as PRXs. I can tell your clueless on how to move the clock which explains why Im telling you to research the RCOs and PRx.  The Clock can be moved using "vshmain.prx"  You have to decrypt it first. Using PrxDecompressor. BUT... *if your on 3.90* you'll have to find the "offset" Manually using a "Hex Editor" software. Some are free and some are not its up to you to find a freeware one. In my opinion the best is "Hex Workshop" download this and keep it ^^  Why do you have to find the offset manually? because 3.90 is somewhat fresh released so no GUI (software) is out yet.. But if your lower you can use "vshmain editor" easiest way to do it. But don't worry doing it manually is easy very easy.. Just go to the "3.90 Offsets" thread.  I think is in  PSP Customization.


2. I know looking at those themes is a bit like "@#%" how the @#$%$ will I do that without knowing a thing.  Download theme #1.  Open the RCOs with "Rcoeditor" and go to the 3rd tab and check what their "X" "Y" Position is etc etc. check topmenu_icon.rco and check and look around how the main icons were done and gain some knowledge from that and try to "re-do" what they did. Also those themes will always include "paf.prx" and "vshmain.prx"  If you want use those two files to get the "position" of everything already set... Then just make your icons and your good to go.. (give credits for the pafs vshmain if you want) not necessary if your theme is an applecorp MOD like "Theme #1"



Other than that.. I don't know what else to say :)  Good luck! and welcome to the PSP Scene! you'll enjoy it!