Hey Branitar. Yeah, that keyboard you're using is crud.

Grab this, unzip, and put the folder on your internal memory card.
[ATTACH]Keyboards[/ATTACH]

You'll need to edit the file
/usr/share/Dosboxxkbd (I think)

To do so you'll need root privileges (easyroot) and emelfm2 if you don't have them already.

Change the file to one of the keyboards that best suits you, there's a notes file inside that folder to help you.

Since you're not using Dosbox in full screen, your best choice would be the one that says:
*Left side keyboard with no minimize feature*

So just edit that file and change it to:
xkbd -geometry +65536+65536 -k /media/mmc2/Keyboards/Leftfull.xkbd

If you're having problems doing so, I guess I can go into more detail or perhaps Pushwall can take it from here.

Cheers.