You definitely need more than just an English degree to be a technical writer. You need to know about a technical subject. If you do not have a degree in the technical subject you are writing about, you should be involved with it some other way and still study it on your own. Also, one thing I have notice when I job hunted in the past is that employers don't only want you to have an English degree, you also need to have skills, like software skills and typing. So keep in mind that you need to back the degree up with additional skills and knowledge.