How hard is it to make a launcher?

I have no programming experience whatsoever. I'm familiar with a couple terms, but let's just say there's nothing.

I know the launchers are made with NSIS and I basically know what NSIS is - Nullsoft's install system, literally. But how hard is it to actually do the coding?

I read the 'guerrilla field guide' a couple times, and had a question: Is it saying to take one of the existing installers and just change it up some? I suppose that's not a problem if it's open source. And I might be able to do that. I decompiled the game I'm interested in making a launcher for (using the SDK - this is legal) and I've tweaked a few things. I can tweak. I've been able to skyrocket the ammo capacity the player can hold, among other things. No more "you have enough of this ammo" messages (unless you cheat). And that involves decompiling and recompiling, and I guess an SDK and the NSIS compiler are comparable somehow.

One big hurdle I think I'm gonna run into is admin vs. limited access. The game runs great off my flash drive, but it takes 2-3 minutes to save and load (which it does every time you go from map to map). So it would be really clever if the launcher were to copy the save folder from the flash drive to the C drive, utilize the C drive for saving while the game's running, then when you quit, move it back to the flash drive. Trouble is, in Vista, you have to have admin access to write to anything but the Documents folder, which differs between XP and Vista. Where the game saves is taken from a line in the game's INI file - would the launcher be able to detect the OS and the user account level and modify the INI accordingly so the game will work fine from XP to Vista and back again?