Something like that should work, not sure if what you did does, though. You could look for emendelson's (search the users posts here) copy/paste thing for Windows. I think he uses autoit as well.
At first glance I'd say though that it should reference dosbox.exe rather than "Dosbox 0.74"

ehdium wrote:

I'm using AutoIt3 to run a script like this:

ControlSend("DOSBox 0.74,","",0x00080210,"W")

with no success. So I ask: have you had success in sending keystrokes to a DOSBox window? If so, how?

Just use Send, not ControlSend. Something like this works well:

1If WinActive("DOSBox") Then
2	Send("{TAB}")
3EndIf

You'll need to use WinActivate("DOSBox") before running that code.