Great I'd recommend using a different assembler, though. I use spasm. It's much easier, faster, smaller, less buggy, and more powerful/flexible. Another popular assembler is Brass.

I'm just waiting to get my hands on one. Finding a way to run machine code is quite a bit over my head, but once we get there i'll be more active

That's how all the old programs that let you use 100 strings/pictures in BASIC programs worked

I don't know all the fancy terminology, sorry, someone else can probably fill you in on that. Essentially _PutS reads the string from the address in HL, but an application is stored in flash (in the memory bank that covers $4000-$7FFF). When you jump to the bcall, the flash page that was loaded into that memory bank gets swapped out and the page the bcall is on gets swapped in. Thus the string that was in your application is no longer loaded at that address. _PutC draws the character loaded in the accumulator (a) so you don't have to worry about all that. Another option would be loading your string into safeRAM before calling _PutS.

I would quit programming on-calc and use spasm or brass to assemble with and TilEm2 or WabbitEmu (or even PindurTI) to debug. What exactly do you need help with? Setting up the hook? Coding the menu?

EDIT: From the information on WikiTI i just built a quick program (well, app) to install a raw keyhook to check if Prgm was pressed.
To assemble you'll need ti83plus.inc and app.inc, attached. To assemble you might need to download spasm.
#include "ti83plus.inc"
#include "app.inc"

defpage(0, "PrgmMenu")

start:
bcall(_ClrLCDFull)
bit rawKeyHookActive,(iy+sysHookFlg) ;check if hook is active
jr z,activate
;uninstall hook
ld hl,uninstalledTxt
call AppPutS
bcall(_ClrRawKeyHook)
jr quit
;install hook
activate:
ld hl,installedTxt
call AppPutS
in a,(6) ;load the current page into a
ld hl,prgmMenu
bcall(_SetGetKeyHook)
quit:
call pause
bjump(_JForceCmdNoChar) ;ciao!

AppPutS:
ld a,(hl)
or a
ret z
bcall(_PutC)
inc hl
jr AppPutS

pause:
xor a
out (1),a
push af
pop af ;delay for slower calcs
in a,(1)
inc a
jr nz,$-3 ;wait for all keys to be released
in a,(1)
inc a
jr z,$-3 ;wait for a key to be pressed
ret

installedTxt:
.db "Hook Installed!",0

uninstalledTxt:
.db "Hook Uninstalled",0

prgmMenu:
.db 83h ;required byte
cp kPrgm ;check if [Prgm] was pressed
ret nz
ld hl,noMenuTxt
call AppPutS
call pause
bcall(_ClrScrn)
bcall(_HomeUp)
xor a ;set z to ignore keypress
ret

noMenuTxt:
.db "Haha! Now you   have no menu!",0
I'd never used hooks before, either, but the information's out there

I also think the grass moves too quickly, i'd cut the speed at least in half. Btw, are do the animations continue when the player is moving (unaligned)?

I don't think Xeda meant that tilemapping was difficult to do but rather that their code might be a little difficult to dive into if you aren't already familiar with it and how everything works.