Meller's chameleons aren't necessarily "harder" to keep than any other chameleon, but they have very specific care requirements that must be met if they are to survive. WC specimens are heavily parasitised, also with possible blood born pathogens etc.
Go for a captive born, or c. hatched if possible. Mine are WC, and needed alot of medication and tlc to bring them back to health. They can overheat very easily, so temps need to be in the mid 70's with a basking area that wont heat up the rest of the cage. They usually wont drink from a dripper, so they must be hand sprayed multiple times daily for up to 20minutes, or even better an automated misting system that will spray onto their favorite perch area. They are very intollerant to stress, so they require very LARGe hevily planted setups, or better yet a free range room with lots of plant cover.
I've heard free range setups make them much more tollerant to humans.
They are also very picky eaters, especially wc specimens. I have to rotate silkworms, roaches, superworms, etc.
to keep them interested. If you have the patience, they have awesome personalities, but they do need alot of time and care.
There is a meller cham. group on yahoo, you should check it out
http://groups.yahoo.com/group/mellerichams/
gw