First of all, make sure you have turned on TYPE,DEFINE,GLOBAL extended syntax (edit>edit options>[editor options]tab) otherwise DB won't understand the additional darkedit commands. Note that GLOBAL extended syntax MUST be enabled as well as TYPE.
Then try this code:
TYPE player_info
x,y,name$
inventory#(10)
ENDTYPE
DIMTYPE player_info,player,enemies(20)
player.name$="y"
enemies(15).inventory#(2)=2.3
PRINT player.name$
PRINT enemies(15).inventory#(2)
If you've turned on the options correctly darkedit will show you a dialog box [before it runs DB] telling you it has found the TYPE declarations. Click continue & DB should work as expected with the extended command sets.
Also there are some notes on the DIMTYPE notation hidden near the bottom of the darkedit.txt textfile.
hope this helps!