By far the easiest way of getting Ioncube working on a DreamHost hsted site is to use their own IoncubeLoader Installation script, which can be found here:

http://sxi.sabrextreme.com/dh-phpion

Simply upload a single script and visit it with a browser. Job done, although be warned that it will rewrite your php.ini file and an .htaccess file. If the link above doesn't work, just try Googling for dreamhost ioncube installer' and it should come up somewhere in the search results.

You can also find out more about Ioncube installation on DreamHost here:

http://wiki.dreamhost.com/IonCube_Loader