That one won't work without resizing/proper placement on the charset "grid", never mind color depth, which can be fixed by opening it in MSPaint and saving as a 256-color bitmap.

Your charset is 146x204, charsets in RM2k3 must be 288x256.

They also have a "grid" that is rigid as well - your charset has 4 animations for each of the 4 directions (36.5x51) - RM2k3 has 3 animation frames (24x32 each) per direction, and 8 characters per sheet (the others can be blank if needed). As a sidenote, I have no idea how a charset with a width not divisible by 4 works in XP...

Yeah, that one won't work in RM2k3 without a bit of work.