Lost in Translation

[Aegis]

The game won't run in DOS, so no. But you can do it from the terminal (Start -> Run -> cmd). It's easier to use a shortcut or .bat file, though. Just make an empty .bat file in your M2TW folder and write this line in it:
medieval2.exe --io.file_first
Or, create a shortcut to medieval2.exe, right click it and select properties, then change the destination to "[some path]\Medieval 2 Total War\medieval2.exe" --io.file_first (note the location of the quotes).
Or, finally, open your medieval2.preference.cfg file and add the following:
[io]
file_first = 1

[Feldmarshal Arcadies]

Okay. Not entirely sure what a .bat file is, but I'll give those a shot. Much obliged and thanx.

[Feldmarshal Arcadies]

Though curiousity compells me to ask. What exactly am I telling the computer to do with all this "--file_first" stuff?

[Aegis]

A batch file (extension .bat) is just a set of commands to be executed. If you create a batch file and write a couple if lines in it, it will upon execution essentially act like if you had written those lines into a command interpreter (such as DOS) yourself.

For example, a .bat file with the following in it:

cd..
cd..
dir

would go up two levels (from the folder it was executed) and print out the content of the folder it ends up in.

The file_first stuff is just there to tell the M2TW program to read data from the files you've unpacked (and modified), rather than from packs that are not edited.

[DarkKnight]

To make a bat file just write it up in notepad, but when you save it as, put .bat at the end of what you call it.

[Feldmarshal Arcadies]

Well, that just clears up everything. Thanks guys.