2.1 rooted rom help

[droidism]

I am still trying to grasp the vast and overwhelming world of the rooted droid...I first want to thank all of you who have infinate patients with the newbs. I would be lost without you...as would alot of others lol.
Now to business, I was wondering, my droid is rooted with 2.1, I have bb1.0, overclocked to 1.2ghz, etc. I guess my question is when you install a custom rom is there a way to completely modify it to make it your own?
I love bugless beast and applaud Pete. But I would like to change icons like the battery or the menu screen etc...I guess kinda pick and pull from various roms and put everything together.
My second question is, When going from one rom to another, based on the size of each of them, how can I go through and erase them from my sd card. where am I looking?
what am I looking for?
how do I distinguish between them and other files?
I really appriciate the help...
Please feel free to poste your custom droid screens I would love to see what people have done.