I live in the DC burbs and drive up to northern New England a few times every winter. I stay away from I 95 like the plague. My suggestion is to go west, up through York PA and Harrisburg PA. If you get on Rt 15 North from Leesburg VA, it'll take you past Emmitsburg MD, which is anly about 10 minutes to Liberty. The further north, you'll be close to Roundtop. Also, when you get up further into PA, Montage (don't know if I spelled that right) is just off the highway. Then, I think West Mountain is up in NY or CT or somewhere up there, just off the highway. I've heard good things about their night skiing because of their extensive lighting.
If you want to go up to the northern boarder of PA, Elk mountain is good.
That said, if your plan is to go to NYC, you might be better off on I-95 since it dumps you into the city. The option would be to stay west, then at Harrisburg, take I-84 east through Allentown PA, to NYC.