You can do it by events on XP, unless you want custom keys.
For both RPG Maker XP and VX, there are keys assigned to certain letters. Let me explain:
Here it shows 10 options. They show letter A, B, C, X, Y Z, L and R. Meaning you can have up to 8 different keys.
Then you assign each keyboard key to these letters.
In the original configuration, Enter, X and Spacebar are the "C key". Esc, X and 0 are "B", Shift and Z are "A". A is "X", S is "Y",D is "Z", Q is "l". W is "R".
What you can do is this: Only A, B and C are used by the game originaally, so you can use X, Y, Z, L and R freely. That means the keys A, S, D, Q and W are the ones you can use, if you keep the original RMXP configuration.