Thieves Guild Quests
There are no non-member Thieves Guild Quests. Of the 15 quests available to members, there are 4 that are available only while your rep with the guild is 20 to 29. If you want to make them all available, you need to rename the files. They are currently named "\dagger\arena2\O0b2xy*.*". If you change the file name to "\dagger\arena2\O0b20y*.*", they will always be available once your rep is 20 or more.
Thieves Guild quests never involve dungeon crawling. Everything is done on the town maps. This makes the quests quick and dirty, so it's very easy to repair your rep when you do some other quest that crosses the Thieves Guild.
Membership Quest: you activate this quest by stealing things, pickpocketing or breaking into a store without using an "Open" spell. It requires several attempts to steal or pickpocket, but only one success at breaking and entering. The quest will launch 10 days later and arrive in the form of a letter accusing you of being a thief and telling you to join the guild, or else. You will be required to travel to some town, break into a particular house and steal an item of clothing. The item belongs to a mage (who is usually not very happy about your stealing his stuff) and it's going to look like a pile of clothing on the floor. Pick it up and you'll get the item and a slip of paper with a name and town on it. The order is always name/location. Take the item to that person and you'll be admitted to the Guild, receive 1 gold piece for your troubles (this doesn't work) and the location of a dungeon on your overland map.
"...we got one of our family who's in trouble..." (any rep) and (rep 10 or more): the contact is usually in a tavern, but not always. Simply travel to the town, click on the person and report back to the Guild. About the only ways you can blow this quest are to let the time expire, keep the gem for yourself (whatever happened to "honor among thieves"?) or talk to a town guard while you have the gem in your possession.
"...all you gotta do is bring this <item> over to our agent..." (any rep): go to the town, talk to the contact, bring the gem back to the Guild. Don't talk to the guards while you're carrying the item.
"...a simple game. An item in a house that needs lifting..." (any rep): This is a tough one. The house will be in the town you are in, but there are guards to deal with. The major problem with this is that a guard is usually right inside the front door and you appear INSIDE him when you enter. Fighting the guards blows the quest. If you can get your hands on a potion of Invisibility or have the spell, Invisibility or Invisibility (True), you can get past the guard, get the item and back to the guild with no problems.
"...A little package needs delivering to <town>..." (any rep): there are four possible ways for this one to pan out. When you get to the town, you will either find your contact in the house he's supposed to be in or you will get a message telling you to meet him in another town. In either event, you might or might not run into thugs who try to take the goods away from you. Hang around and fight the thugs if you want (they usually aren't carrying anything worthwhile), but report back to the guild before the time expires.
"...Got a guild job for ya, if yer innerested..." (rep 10 or more): steal an item from a temple and bring it back to the guild. The only problem with this quest is that sometimes there is a guardian in the temple and sometimes not. Also, your rep with that temple order will take a hit.
"...You remember me, <name>? Are up for a guild job today..." (rep 10 or more): travel to the town, break into the house, lift the painting and report back. Sometimes there is a guardian, sometimes not.
"...Jewelry heist in the works..." (rep 10 or more): go to the town, break into the house, steal the jewelry, report back to the Guild. The dialogue says that there is a guard, but it's kind of an iffy thing (at least on my system).
"...We have had our eye on you.... Never mind who "we" are..." (rep 10 or more): a good quest, especially because it boosts your rep with the guild by 10 points rather than the usual 5 points. Go to the town, break into the palace, lift the item (it looks like a piece of dungeon dressing, but shouldn't be too difficult to spot), report back to the guild. If you're feeling adventurous, there are usually a couple of paintings in the crates in the back room of the palace that you can lift, too. Opening the crates will often bring the guards, but all you have to do is get out of the palace before they hit you (a walk in the park for any competent thief).
"...Keep your voice down. My name is ..." (rep 20 or more): steal the magic item and report back to the guild. Maybe there's a guard, maybe not.
"I have a job. Ordinary guild work..." (rep 20 to 29): steal a book and report back to the guild.
"...I have <gold> for you if you will steal some <drug> for me..." (rep 20 to 29): steal the drugs and report back to the guild. If your conscience gets the better of you, you can ask around and find out that the guy you're stealing from is a drug dealer.
"...I have wind of some <item> that some pig of a merchant just bought..." (rep 20 to 29): steal the item and report back to the guild.
"...I have a line on a <ingredient>. I need someone to lift it for me..." (rep 20 to 29): break into the alchemist shop, steal the ingredient (sometimes it's a potion) and report back to the guild.