Tess, if the item thumbnail is red, this means that the sim family doesn't have sufficient funds to purchase the item.
I have seen other threads where members mention having problems placing doors on some downloaded lots. This is usually due to a vidoe driver error (updating your video driver may correct this) or the lot was made with a EP for the game which you are missing. Sims2Pack Clean Installer allows you to install houses that are incompatible, so isn't necessarily the best tool for installing houses.
Also, make sure you update your game with the latest update patch from:
PCs:http://thesims2.ea.com/update/Macs:http://www.aspyr.com/This may help.