There are any number of potions out there to turn Sims into (or cure Sims of) vampire and plantsim, such as:

http://www.insimenator.org/showthread.php?t=38901

http://www.modthesims.info/download.php?t=201384

(Lots of others which regular searches will turn up.)

Or one can use objects (such as Insimenator) to change them or to change them back.

But gonna give you links to some more unusual items/methods (besides the plethora of potions).

Sim Transformer:  http://www.modthesims.info/download.php?t=283201

Plantsimenator ($$): http://simslice.com/thesims2/guests/wintermuteai1-pg5.htm

Or at the booty (simslice-ts2-plantsimminator.zip): http://paysites.mustbedestroyed.org/booty/ts2/simslice/wintermuteail-guest_artist/

Vampire bat edibles ($$): http://simslice.com/thesims2/ts2objects-pg9.htm

Or at the booty: http://paysites.mustbedestroyed.org/booty/ts2/simslice/objects/vampire_bats/

I'm kind of partial to the vampire bat edibles, as the occasional hungry visitor will nibble on them, too.

As for becoming a plantsim without using hacks, use herbicides enough and keep aspiration up and it'll happen.

For whatever it may be worth, there's one at the Exchange (reg. req.):

http://thesims2.ea.com/exchange/sim_detail.php?asset_id=450458
.

It is listed as included with this house:

http://www.modthesims.info/download.php?t=242233

Using Clean Installer, you could install just the portrait without having to install the entire lot and its other content.

Take a look here:

http://fantasylostworld.online.fr/Sims2/Skinsjeuxvideo/Sims2SkinsFF.htm
.

Not Rebecca, not MTS2, but here is a bigger family mod which works with none, any or all EPs, including AL:

http://drupal.cyjon.net/node/141
.

Don't know if either of threse may be the one you remember, but take a look --

Zita's Designer kitchen (scroll down a bit to get to it):

http://www.aussietopenders-sims2.com/newmeshsetspage2.htm

Paris kitchen--

Pay: http://www.stylistsims.net/sims2/donation_05.html

Booty: http://paysites.mustbedestroyed.org/booty/ts2/stylistsims/

Take a look at this page:

http://www.simpathetic.com/fashion.htm

A lot of Chriko's (2-4-U) meshes are included with outfits there, and there are some jeans on the left side about 3/4 down the page. But those may be adult meshes, not teen.

Take a look at the links listed in this message (except for the first site listed there, as that site was scheduled to go away at the end of August):

http://www.insimenator.org/index.php?PHPSESSID=5afc5a0ca2c885b68af7614341a97edc&topic=107013.msg1559654#msg1559654

And you might find some large/larger houses you can use here as well:

http://www.xn--hg-gkaw.de/houses.htm
.

Among other sites wiuth nose masks, a colection of 40 at Sirona:

http://www.sironasims.com/40-multiwearable-nosemasks-for-creating-unique-and-beautiful-sims.html
.

Maybe this? (It is cloned from the crib.)

http://www.modthesims.info/download.php?t=121652
.

Several varieties of wheelchair for toddlers throughout both pages of this thread (but free reg. req. to see pix and download):

http://www.simsafe2.com/forums/index.php?showtopic=1491
.

There are pre-made college 'hoods out there, but I tend to using custom empty 'hoods and building on them specifically to make a college I prefer, using custom Greek houses, custom Sceret Societies, etc.

So I can't point you to any pre-made colleges/universities with which I've any experience, but can point you to a place with some empty custom terrains I've used for college 'hoods (not the biggest selection, but an interesting mix):

http://www.angelfire.com/va3/elstonebyrequest/ed-ter-riv/edterriv.html

http://www.angelfire.com/va3/elstonebyrequest/ed-ter-nov/edternov.html

And just to make sure (apologize if question is too elementary), you are putting custom terrains into the sc4Terrains folder and not into the Downloads folder, correct?

If I understand what you are saying correctly, this problem happens only with a custom 'hood and not with your regular 'hoods.

That could well point to the source of the problem being the custom 'hood itself, especially if it is a custom 'hood which requires EPs/SPs which you may not have installed.

Two questions:

1) Are you by any chance trying to build a dorm in a 'hood other than a college/university?

2) Have you used the changeLotZoning cheat on an occupied lot? (That's a big no-no.)

Not invisible, but might something like this do?

http://www.modthesims.info/download.php?p=1600122

Have an even nicer one in my game, but unable to determine where it came from just now. If the light bulb about that particular object goes off, will add via edit.