I've made a yahoo calendar where I'm filling in the dates when friends and family will be visiting this summer. Most of the dates are still tentative, and in some cases (like with my Parents, and my friend Pat), I've listed their entire traveling dates but they'll only spend a bit of that time with us (just don't know which bit yet). I'll put question marks with the entires that are not confirmed dates yet. Then the rest of you can figure out when you'd like to visit as well.
I think everyone should be able to see the calendar without issues, but let me know if that's not the case. I'll also make a link to the calendar in the menus off to the left.