Success! I've managed to unlock everything in the game now... And for those still wondering how:
(Helpful hints: holding the ctrl key lets you speed through things you've already seen and ctrl-space repeatedly skips through new stuff sans sound and quickly. You also have far more save slots than you can possibly use; take advantage of them. Also, you can waste time in-game when given the option of which girl to chose by picking the second option from the bottom.)
First off, play through the game with all four girls, getting their individual endings. Note that the percentage bar in the corner indicates the girl's mental state; her level of transformation is solely based on the number of times you've taken her to the OR and played with her. Additionally, you'll need to make sure you have access to all the normal CGs of each girl- you can check which ones you have by choosing the second option from the main screen and the first option after that; blank ones are things you don't have yet, grey-screened ones are incomplete, generally because of there being multiple path choices. This whole thing will take a little time and probably require a strong stomach, depending on your tastes (or lack of such). You should now have all but the last two CGs for everyone unlocked.
As part of all that, you can unlock each girl's two extra endings. Normally, the ending shows the girl in her "normal" state; the extra endings play off of the transformations you've done. On beating the game with a girl, wait for the beginning of the credits screen (white with a bunch of Japanese characters, some colored) AND MAKE SURE NOT TO SKIP PAST IT VIA CTRL/SPACEBAR. Right-click here and you'll be rewarded(?) with an additional scene featuring your girl; there's one for each of the two tranformations for the girls- you have to have taken that path to get that ending.
Finally, the purple-haired chick. I'm still a bit iffy on exactly how this works, but I'm pretty sure you have to have all of the normal CGs unlocked (everything but the additonal endings). You'll also need to get two girls all the way through their transformations (i.e. complete all the sequences- it shouldn't matter which of the two branches you choose). Here's the sticker, though- you MUST NOT get any of the girls to 80% or above. Yes, you must fail at your job in order to get the final ending. Now, here's where it gets fuzzy- I unlocked one of the girl's extra endings the same game I got the purple-haired girl, but I can't say if that's nescessary. But hey, no reason not to. Anyways, following all the normal stuff (credits included), you should get a long sequence of talking with the blonde guy that keeps showing up, followed by some tearful talking where doctor lady confesses that she's always loved you and was doing all this stuff for your sake. You of course respond by transforming her. A right-click after her (relatively short) sequence will give you one final scene involving all the girls together. And now you're finished!
As a final bonus for those struggling with the game, here's some basic directions for the choices in the game:
You initially don't have many choices. Run through with the red-hair girl, intros to all the characters (which are forced), and an inflation bit with red-hair again. Now, you have a chance to walk around to various places. ALWAYS chose the first option in your office, which brings up a menu of the girls/locations.
#1: Red. You always have her, as Leviathan noted. Her paths split to **12**/general inflation.
#2 Purple. (Young.) You can decide to check up on her or not (in that order.) Her branches are.... something and mkaing her very "stretchy." Ugh.
#3 Blonde. You see her in the hallway and she asks you to help one of her patients (with no/yes choices.) Her path splits to either nipple-dicks or just one huge one.
#4 Green. She yells at you for staring at her body and is generally just very angry at the world. Options are yes/no, representing something I don't quite know. Her path branches into making her "acessable" to many men or giant, milking breasts.
#5 Don't know what this says, but it basically just wastes a day.
#6 Examine the girls' profiles.
You'll also occasionally get another option, which takes you back to the previous menu. If, at the beginning, you declined a girl's path, they are absent from the menu.
Gah. That's enough of that for now.
-SMAP
"Superman moves the Earth around a lot, and whenever it happens, we see a shot of it from space. He flies away from the camera, disappears into the distance, and the Earth starts moving. Easy. But to anyone standing next to Superman at the time, it would just look like some guy in pantyhose was doing a handstand. And if he told you he was saving your planet, would you believe him? No, you'd run like hell and call the handstand police to give them the case of their lives."