Even though my major is IT/ web development I have only learned enough about css, xhml, asp.net, php, js, and mysql to make me feel like I will never learn how to put it all together.

How long have you been majoring in this? None of your classes have ever combined two or more of the above tools? Will that be covered in a future, possibly project-focused class? Or you may mean "how to put it all together" in some other context I've not recognized.

Does it require a CMS?

It probably requires at least a templating framework, but may not require something as heavy as Drupal. You certainly don't want to hand-write PHP or HTML for each page.

Will drupal work for a site where a huge database of ‘green’ facts can be accessed, compared, and presented so that users can make buying decisions?

Drupal can probably do most everything, including making breakfast. There is this list of evaluation/rating modules that may help if you want your users to contribute their own opinions. If you're looking to publish a list of costs, efficiencies, etc. of items from a database, then you may just want to go with a more focused framework like Ruby on Rails or Django. I have no direct experience with either, by the way.

Do I forget all that and buy some server space somewhere and build everything from scratch (CSS,Mysql, PHP, XHTML, etc)?

I may not know that much about Rails or Django, but I do know that writing raw SQL and PHP code is no way to live. And you will need to get a non-.Mac hosting account to do much of this.

(You can also check the "theoretically related" discussion above about one writer's similar questions. I won't swear I've got the right answers there, but they're apparently not so horribly wrong to have caused several people to jump in behind me with opposite opinions.)