I've been off for about 2 months, mostly because winter and the holidays kicked my motivation in the shins, but I signed up for a new race and am getting back into it.

I say do a test run to see about how much you can still do and figure out what week to plop back down in to. I found that I only fell about a week behind where I was when I dropped out, so you might be pleasently surprised, especially if you've kept on the elliptical and everything.