VisElEchNon: Well, the GOG application IS DOSBox. The documentation does say that 'O' is supposed to open doors though. Have you tried getting a key and using 'U' on a door. I seem to remember that being what needed to be done.
I'll test it out shortly and let you know.
EDIT 2012/11/30::
Okay, I've tested it and it's working fine for me. I hit 'O' and then the arrow key in the direction of the door and it opens, unless it's locked. If it's locked, it says "can't" and then I have to use a key ('U', type 'key', [enter]).
I haven't gotten an error saying "Bad command" at any point though, so I'm not sure.
Knight_of_Wine: U is for use items, I'm inside a rented room at Jhelom, the door is not locked.
I press O and receive the "Bad Command" message.
Umm did you press O and a direction?
Also in order to unlock a door and enter you need to buy a key from one of the two "guilds" one can be found in Buccaneer's bay the other is in Vesper, make sure you buy more then enough for doors in Ultima 4 will reset as soon as there off screen, you may also want to pick up on reagents while your at it and mix up some dispel spells(boy that sounds weird), you will need Black pearl, Sulfurous ash and Garlic, as the rune in Jhelom(which is past one of the rooms) is blocked by barriers as well as someone you can help out for some extra virtue points. (figured I would save you some trouble while I was here)
also here is the command list
A) Attack - Attempt to engage thy foe with the weapons thou hast readied (Ready Weapon command); must be followed by the direction of thy foe.
B) Board - Board a vessel or mount a horse.
C) Cast - Cast a magical spell; must be followed by the number of the player who wishes to cast it (not needed in combat or in dungeon rooms), and then the first letter of the desired spell. Note: All spells must have reagents mixed in advance of casting.
D) Descend - Climb down ladder to next level of dungeon or building.
E) Enter - Go into such places as villages, townes, castles, dungeons, and shrines.
F) Fire - Fire a ship's cannons (once thou hast Boarded); must be followed by a direction. Note: Broadsides only!
G) Get Chest - Attempt to open (and disarm, if trapped) chest; must be followed by the number of the player who wishes to open the chest, except during combat and in dungeon rooms. Note: 'Tis wisest to use the player with the highest Dexterity when examining potentially dangerous chests as this lessens the chances of setting off any traps.
H) Hole up and camp - Set up camp to rest and recover from thy wounds. Note: This command may only be used with limited frequency.
I) Ignite a torch - Light a torch for illumination in dungeons. Requires a special item.
J) Jimmy lock - Use a magical key to unlock a sealed door. Must be followed by the direction of the door that thou dost wish to unlock.
K) Klimb - Climb up a ladder to the next level of a building or dungeon, or to reach the surface from the topmost level of a dungeon.
L) Locate position - Requires a special item.
M) Mix Reagents - Prepare material components of spells for later use. Note: Thou must have reagents mixed ahead of time in order to cast any spells. When asked "Reagent:", type the letter corresponding to the reagents desired, and then type [Return] when thou wish to mix them.
N) New order - Exchanges the position of two players indicated within thy party, except for player #1, for thou must lead the party.
O) Open door - Open a door in the direction indicated.
P) Peer at gem - Requires a special item.
Q) Quit & Save (Usable only whilst in the outdoors of Britannia) - Saves the current game status to disk; thou may continue after this command or power down thy computer.
R) Ready a weapon - Equip a player with the weapon of thy choice (if owned) for use in combat.
S) Search - Search thy exact current location for unusual items.
T) Talk - Allows a player to converse with merchants or townsfolk in the direction indicated. (See Special Note)*
U) Use - Use an item thou hast found during play by means of the "Search" command.
V) Volume - Toggles Music On/Off.
W) Wear armour - Outfits a player with the armour of thy choice (if owned) for defense in combat.
X) Xit - That's (e)xit thy current form of transportation and continue on foot.
Y) Yell - Yell "giddyup" or "whoa" to speed up or slow down thy horse.
Z) Ztats - Displays the status and attributes of a selected player; If 0 is pressed instead of a player number, this command will display the lists of weapons, armour, items, reagents, and mixtures. The [F5] and [F7] keys will scroll through these lists, while pressing any other key will return thee to game play.
