Ok, so my review:
Short, cryptic prefix names are discouraged, as they increase the risk of collisions with the prefix of other scripts
x86 architecture is the default, but also the architecture of a prefix cannot be changed once it has been created, so as written it happens too late to have any effect.
POL_Download "http://rpgmaker.net/content/games/2732/downloads/IMTS_Setup_24.exe" "7025979eb03e9a226e2dd742f0a02db6"
POL_Download saves its file in the current directory, but it's not clear in the script what's the current directory at this point. I'd add a cd "$POL_System_TmpDir" just before, just to make it more obvious and resilient to changes.
Does the game need so many components? It's best to try to trim the amount to the minimum.
I suspect dxfullsetup covers all what dinput, dinput8, directmusic, directplay and directx9 do, but I'm not 100% sure.
POL_SetupWindow_wait "Running setup" "$TITLE"
POL_Wine start /unix "$POL_System_TmpDir/IMTS_Setup_24.exe"
"start /unix" is usually not required, and has drawbacks, try without it.
Also, dropping it may remove the need for the next POL_Wine_WaitExit