Missy, the web-based client seems to be the problem — you are uploading archived plugin files which are then extracted by the server.

I suggest you unarchive the files on your own machine and then use the free and opensource FTP client FileZilla for transferring the files to the server. This way plugins will definitely work.

Read more about using FTP clients at the DreamHost’s FAQ: How do I use FTP to upload my site?