I'm sorry but I really must laugh at this.
I did exactly the same thing about a year ago!!

Or at least, tried to.
I got some way with it, but eventually gave up because it gets really annoying.
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In answer to your question, YES it is possible but, as NS says, you've got to change them and whatnot.
-- Sprites are easy - you just need to scale 'em down and cut off the extra column.
-- Faces can be chopped out of the Battlers for the respective characters.
-- Battle characters are really hard. Unless you know how to make them, it's impossible.
-- Things like Tilesets are easy. You just make your own by cutting bits from whatever you want and putting them together (make sure to scale them down first).
http://zelaron.com/forum/showthread.php?t=33400
http://zelaron.com/forum/showthread.php?t=33423
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http://uk.groups.yahoo.com/group/rpgmakergraphics/
Absolutely nothing worth having there, I'm afraid. Only a few backdrops. I got round to starting, but never finished it.
Backdrops are easy - just resize them.
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http://zelaron.com/forum/showthread.php?t=32836
Not the best of layouts, so here it is all new and sparkly:
The following are the Sizes of the different graphics needed in RMXP, in pixels. It is set out ___ pixels wide BY ___ pixels high.
-- Animations: Each diff. anim needs to be in a [192 pix X 192 pix] square.
-- Autotiles: [96 pix X 128 pix] --> if you open a rm2k3 chipset, you will see big sections for the trees or path. These are about 4 blocks down and are called autotiles.
-- Battle backgrounds: [640 pix X 320 pix]
-- Battlers (the actual character in battle): [from 1 pix X 1 pix --> 640 pix X 320 pix] --> Are just the one graphic, due to front-view battle systems.
-- Characters: [129 pix X 192 pix] --> instead of three things for each direction of walking, there are four.
-- Monsters: [320 pix X 384] --> instead of three things for each direction of
walking, there are four.
-- Fogs: [256 pix X 256 pix] --> things that make the screen all hazy? I never worked this one out.
-- Game over/Title/Transition screens: [640 pix X 480 pix]
-- Icon: [24 pix X 24 pix] --> these show what an item looks like in the shop
window
-- Panoramas: [480 pix X 480 pix]
-- Tilesets: [248 pix across (in 32 pix X 32 pix squares), by any number down] --> AS LONG AS IT IS A MULTIPLE OF 32!!!
-- Custom graphics need to be saved as "bmp" (bitmaps). Other formats may work as well.
-- To put your custom graphics into RMXP, just create a new project, then go into the directory, find the project folder, open the Graphics folder and then put your custom graphics in the correct folders --> e.g. a Battle background in the "Battlebacks" folder.
All figures have been checked against those on the Enterbrain site and are correct.
-- I have also found the Windowskin...things...on the enterbrain site. They were in Japanese originally, but in English read:
"The window skin is 192 pix X 128 pix. As usually, the PNG file, 32 bits, is used.
Background of A window. Pattern of the 128×128, adjusting to the actual window, expanding reducing, it is drawn. Strictly, around the window 2 pixels each it reaches the size which is made small. This is specification in order to show the window where angle is round naturally. In addition, in the window of part, just this background part being translucent, it is drawn. Because of the translucent window, it is not necessary to make the picture itself translucent.
Framework and arrow of B window. The 16×16 of the four corners is drawn that way, the remaining framework (the part of the side) adjusting to the window, is drawn to tiling condition with thickness of 16 pixels. As for the arrow, the scroll you use as the marker when it is possible contents of the window.
C command cursor. You use in order to display the item which is selected
inside the window. 2 pixels around are expanded are reduced in only
length and breadth, remainder is drawn adjusting to the size of
cursor, level expanding reducing.
D pause sign. You use in order todisplay the button input wait state of the message window. Animation it does in pattern 4 type of 16×16.
E arrow cursor. When selecting the actor and the enemy in the battle picture, you use.
Pattern 2 type of 32×32 is drawn alternately. As for this it is not portion of the window, but it is included in this file of for convenience."
Great translation, eh?
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Hope that helps AoD.
Little Note: The figures shwon above are for making things for RMXP. You'll need to open up different RM2K3 graphics files to find the correct sizes.
If you still haven't worked it out by the end of next week, I'm going to have free time for the next 11 weeks or so (albeit, little bits of free time with giant 8 hour days of Summer Job).