Here's a problem I'd like to see more of: someone has been offered a job AND has an interview at another company next week. The question: should I take the job I was offered or try to go on the interview and see if that's a better fit for me?
Whatever you do, don't take the job offer AND go on the interview, just to see what's possible. I know some people do it, and sometimes it happens that you get two offers and have to make a decision. That's different, however, from accepting a job with the INTENTION of quitting if you get another offer. It's just not the right thing to do, to dump a perfectly good job and leave the employer high and dry and pretty pissed off. Talk about burning a bridge! And bad karma to boot. In this economy, it would be the equivalent of job suicide to do so.
In another economy, I might suggest trying to delay your decision until you have the interview, or asking if you can move up the interview. Two challenges with this: the employer who's offered you the job has TONS of other eager applicants just dying to take your spot IMMEDIATELY. And the other employer knows she holds all the cards and can find someone equally as good as you whenever they get around to doing interviews. This is called an "employer's market" for good reason.
In THIS economy, I think you'll have to make a decision between the job offer and the interview. It's really fantastic and a testament to your abilities and background that you have a job offer AND an HR person interested enough in you to consider you for another job.
My suggestion is to listen to your gut. So here are some questions to guide you:
* Can you stomach doing the job you were offered? Does it meet most of your "Must Have List?" I assume that you want it to some degree or you wouldn't have applied and gone through the process with such apparent enthusiasm that you were offered the job. If you can stomach doing the job, I'd go for it. As the saying goes, "a bird in the hand is worth two in the bush."
* How confident are you that you'd ace the interview for the possible job? In the situation I read about, the person already was turned down by that company. Though the HR manager liked the candidate, she is not making the final decision. In my book, that's too much of a wild card.
* Do you want to work for this company so much that you're willing to take the risk of turning down a "bird in the hand" in hopes that one of the "two in the shrubs" will land in your hand? Can you afford to not work? The job offer is precious, and the job will undoubtedly give you great experience, as well as a paycheck. Is it a perfect job? No. But no job is the perfect job. It's a matter of our priorities and whether a job meets 60-75% of our Must Have List. In addition, we have the power to make anything a fantastic learning experience (think "negative powers of example" as in "I'll NEVER do things that way when I'm the boss!").
As I said, however, it's up to you and your gut feeling. If you really can't stomach the job you were offered and will be desperately unhappy, then don't take it.
You can easily handle the situation so as not to burn any bridges. Simply call the HR person to say that you have great news for you and not-so-great news for her.
"I got a job offer and I've decided to accept it. It was a difficult decision because I am so interested in working for your company, and I thank you very much for believing that I could make a contribution to your company. If it's OK with you, I'd love to stay in touch and perhaps the time will be right at some point in the future for us to work together."
It's polite, keeps a door open, acknowledges her kindness to you, and shows that you are professional.
Good luck with your decision!