I think weight training is very important to runners. In fact, I attribute a lot of my marginal running ability to previous lifting.
That being said, depending on your running experience, once you begin running you're going to sore in places you didn't know you had and the last thing you'll want to do is lift lower body. However, depending on the intensity of your running plan and far out your goal race is, a lower body workout can definitely be done as a cross-training workout once a week.
Some of these guys are able to handle more but, as a beginner, I would say once a week is fine. I know that once my volume and intensity crept up, I have found it very difficult to do much, if any lower body lifting.
I think it also depends on what your actual objective is. I'm training to run a marathon as best I can. I believe weight training actually now affects my running training negatively, i.e. I can't run at prescribed paces. If your goal is to just run it, keep up with the lifting for sure.
This is pretty convoluted and maybe even contradicting.

Wait for the experienced guys for more information. This is just what I've noticed from the short time I've been training for running.