If anyone needs a guide to how text adventures work, the basic command abbreviations are:
n, s, e, w for north, south, east, west
u,d for up, down
i for inventory
x (object) to examine an object. Try examining the girl's bodyparts...
There are also some special commands in this game, like 'limits' or 'daydream'. Check the notes.
You could also check out http://www.brasslantern.org/beginners/
Spying on Miss Holloway: if you've found her address, you need to find a good vantage point. Try looking in the alley behind her house.
The keys for the office: Alison will give you those, if you take part in her plan. To get inside you will need to wait until the head leaves his office.
I've no idea about spin. It could be a default TADS command that isn't implemented in the game at all. It's possible the game at the party was going to be 'spin the bottle' so the spin command was implemented for that reason. SD3 does have a convoluted past in that Goblinboy partially wrote a sequel to the first game in the series (Camping Trip), decided the sequel wasn't going the way he wanted, released that game as SD2 anyway, and then reused some of the code for SD3.
The threesome with Becky and Molly at the end requires both of them to be in love with you (if you need any specific hints about that, pm me). You don't have to be drunk at all. The topic of threesomes then has to come up during Truth or Dare. Then, when Molly says she wants to have sex with you, you initially have to leave with Becky.
You can also have a foursome with Molly, but since the other participants are Mike and Gary, that's possibly not as attractive.
I'd also suggest having a look through http://groups.yahoo.com/group/aifarchive/ if you're stuck for hints about something, as SD3 generated a lot of discussion, so chances are that your problem came up.