For 5 and 2 -

You DO know how to copy/paste a file, right? Just go to wherever you downloaded the PNG to, Ctrl+C it and go to:

C:\Program Files\Enterbrain\RPG2003\project\Game 1\CharSet\

And Ctrl+V it there. (The above folder is for #2.)
For #5, the folder should be:

C:\Program Files\Enterbrain\RPG2003\RTP\CharSet\

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And I'd like to test that file myself, if you don't mind, so attach it to your next reply.

Quick question, what version of RM2k3 are you running? (Go to Help-About) I'm running 1.06.