We have a couple of our wiki articles that may be of some use to you:
http://wiki.dreamhost.com/Image_Magick http://wiki.dreamhost.com/RMagick
Dreamhost VPS no longer allow admin/sudo users.
Also, when you're on a VPS, you can only use sudo with an admin user. If you don't already have one set up, you can set one up from your DreamHost panel here: https://panel.dreamhost.com/index.cgi?tree=vserver.adminusers&
Hope this helps! If not, please don't hesitate to email our support team from your panel. We'll be happy to help, 24 hours a day, 7 days a week. :)
Ellice S
DreamHost Staff