Here's some more info for the Girlfriend Guide...
Denise
Maintanence = High - She calls a lot and if you don't go out with her frequently, you lose points
Things to do = Go out to Eat - Any fast food place, or Ten Bottles bar
Go for a Drive - Take her to Ballas territory to blast some fools
Go Dancing - Take her to a club and dance you a** off
30% progress = keys to her car (You can still only get in it when she's around) I'll add the name of the car shortly.
40-50% progress = "coffee"
100% progress =
Pimp suitMichelle
Maintenece = Low - She never called me, and I never lost points, but I didn't find her home frequently either
Things to do = Go out the Eat - Misty's bar
Go for a Drive - Drive fast, and do a lot of jumps
Go Dancing - Same as Denise
Let her Drive - Simple. She wants to drive and you let her.
40-50% progress = "coffee"
100% = keys to her car
(Monster truck) and
Racing suitNote: You must talk to Michelle the first time you go into Turning Tricks driving school, or you miss her, in my experience. I've never seen her there except for the first time. Eat before you go a lot of meals before you go, and drive a muscle car.
Helena
Maintenece = Unknown, but she is always home it seems. She is quite crazy
Thing to do = Go out to Eat - World of Coq restuarant in Rodeo
Go for a Drive - Not too fast, not too slow. Drive on country roads, but not dirt roads. She'll yell a lot.
Go Dancing - Ugh
40% progress = Keys to her car (Not sure exactly which car since both I saw outside her house were accesible from the beginning) They are:
Sadler pick-up truck and the Bandito80% progress = "coffee"
100% progress =
Rural clothes which = overalls and a sleeveless flannel. Nice for that Mr T look 
Note: She always seems to be at the Ammunation, no matter when you go to talk to her, but make sure you're wearing clean clothes. She also has weapons in her barn. They are:
flamethrower, pistol, molotov cocktail and chainsawBarbara
Meet her at the El Quebrados police station parking lot, where she seems to always be, and be sure to be maximum fat. 30 large meals at Cluckin' Bell should do the trick for this chubby chaser. Note: Eat about 10 at a time. If you vomit, you don't gain weight, I don't think.
Just for dating her, you get:
$0 bribe to get out of jail+
You get to keep your weapons This seems to last as long as she is still your g/f. In other words, don't kill her.
Maintenance = Unknown. I dated her every day to get it out of the way, so I'm not sure if she calls a lot, or if you lose points for not taking her out all the time.
Things to Do = Go out to Eat - She likes the diner in Tierra Robada
Go for a Drive - Medium speed on dirt roads.
Go Dancing - I suggest San Fierro, and drive very fast.
50% Progress = Keys to her car, which is:
Police Ranger65% Progress = "coffee"
100% Progress =
police uniformMillie
First off, I found her home anytime between 12:00 and 20:00 every day, not the time listed earlier. If she isn't home when you go, I recomend driving around her block until you do see her. But she always popped up at exactly 12:00 for me.
Dating Millie the easy way... Simple. Wear the
Gimp suit not the Pimp suit. This gave me "coffee" on every date I had, and a whopping 10% progress each time!
Things to Do = Go out to Eat - The Vine bar suits her. Located in the Old Venturas Strip area, but why bother? Just use the tip above and get her done in half the time

35-40% Progress = Key Card
50% Progess = Keys to her Car. Which is:
a pink Club100% Progress = Nothing, zip, zilch. Having already obtained a new outfit before dating, I assume that to be why.
I'll recommend this also: When dating a woman, do nothing else. Go on a date, save, go back to her place. It's much easier than trying to do missions and show up at her place when you have time. Boring? Yes. Easier? Definately. This way, you only spend about an hour in real time, give or take, to get her to 100%.
And I'll add this about weight and muscle... To gain fat, simply eat a ton. I only needed to eat about 20 large meals at a fast food place to get fat enough for Michelle (Watch out, or you'll puke if you eat too much at once). As for getting thin, don't eat. You don't have to be exercising, I lost muscle doing the driving tests at Turning Tricks. Eventually the game will tell you that you are getting hungry. First you'll lose any fat you have, and then you'll start losing muscle. It takes a while, but it drops faster as more time goes by. Also of note, if you have muscle and eat to get fat, you retain the muscle. *And you don't need to maintain your body type after you get the first date!*
Percentage Breakdown
(You start with 10% just by being in the girl's vicinity, it seems)
Meet for the first time = +10%
First Date = 0% (?)
Succesful date = +5%
Succesful kiss = +1%
Succesful gift = +1%
"Coffee" = +0-5% (Doesn't seem to be a way to influence it. Seems random)
Get Lost = -5%
Unsuccesful date = -5%
Accidents = 0%
Gift/Kiss Refusal = ?
Negative "coffee" Response = 0%
(Any info on how her refusing a kiss or gift affects progress is appreciated. I've not paid enough attention to this point, but will next time. The first date I went on with Barbara gave me 0% progress, not sure if that's common or not.)
I'll add more as I get to them. Any of the girlfriends not listed, I haven't gotten to yet, but I'll post about them when I do.
And these are only my experiences. I don't intend this to be absolute, just a guide of what happened when I played.
This post has been edited by Code 187 on Monday, Nov 8 2004, 10:05