to the cursor concept-- its near impossible, it never works good in real games.
there is nothing a hard reset wont clear up on a calc. you can crash ur calc in wicked ways but that's just about it when it comes to fuxoring something. although with the newer flash-based calcs you can overwrite the os, but thats what the firmware is for (loading os). the firmware is in rom, read only and unerasable.
and a tad of a reality check here- on the z80 series(es)(ti-73,81,82,83,83+,84, 85,86) the max program size is 24k, on a tiny screen with _weak_ processing power. on the 68k series(ti89,ti92+, voyage 200 etc) it is 64k, but there is ways around this. but keep in mind that the 68k series still is not much more powerful, although it has a larger screen.
bottom line: keep dreamin =/