I went to college in Williamsburg, so I have plenty of advice! More than I care to have, actually.
You have quite a few options. First, there's Busch Gardens Williamsburg (now called BG Europe) if you're not already burned out on theme parks. I sure wouldn't want to go there right after Disney, but just in case you didn't know, I thought I'd mention that.
In Colonial Williamsburg (CW), you can take a variety of tours and the like. If you're pressed for time, you can just walk around. You won't get in some "tour only" buildings, but there's plenty to see down and around Duke of Gloucester Street (called DoG Street by the college crowd). It's going to be packed at that time though. I'm pretty sure there's some kind of fireworks display that night on DoG street, so you could see that at the least on your travel day. And may I suggest the Cheese Shop on DoG Street for good sandwiches for lunch (the baked ham is especially yummy), and Aroma's coffee shop/cafe on the street behind it has great desserts and smoothies. Barnes & Noble is there as well, and they have their standard cafe. Wythe Candy Shop is expensive but has some great, hard to find candy.
Jamestown you have 2 options. What you think is the real Jamestown and then the
real Jamestown. The Jamestown with the ship replicas, fort, American Indian village and the like is great to visit, but it's not actually Jamestown. Jamestown (the real one) is found on Jamestown Island, a little ways past the replica up Jamestown Road. I believe it closes at dusk or dark, and it's run by the National Park Service, if memory serves me. I haven't been to the island in a while, but it's not expensive and last time you could see the archaeological dig of the real fort (which some of my professors worked on). Plus there's displays, a church, and remains of various buildings. There's a visitor's center there as well. If forced to choose, I'd go to the actual site. It's neat to see the replicas, and to feel like you're there, but it's much more interesting to me to know I'm standing where it all happened.

As for the replica, I'm not sure what's open and what's not at the moment. They're sprucing a lot of things up and building things for the big (or maybe I should say huge) 400th celebration next year.
It really all depends on what interests you. I suggest you look at the following sites and then go from there:
Jamestown Island
Jamestown Settlement
Colonial Williamsburg
If you get a chance, drop by the College of William & Mary's Wren Building for a quick tour. It's the "oldest educational building in continuous use" in the United States. Thomas Jefferson and others took classes there. I was lucky enough to have a class there my senior year (hated the class, loved the building

). Not sure if it's open for tours in July, but it can't hurt to ask. It's the main building visible from the shops' end of Duke of Gloucester Street.
Wren Building W&M's the 2nd oldest university in the U.S. behind Harvard, so it's neat to look around that front section of campus (what students and alum call "Old Campus;" the newer, tackier section from the 70s or so is "New Campus," and most people hate it, LOL).
Hope this helps a bit. There are plenty of restaurants on Richmond Road as well. Off the top of my head, there's Ruby Tuesday, Olive Garden, Friendly's, Outback, Chilis, and Kyoto (a Japanese steakhouse). There's also the Williamsburg Pottery up the road if you like crafty kinds of things and want to stop in on your way out. Have fun, and let me know if you have any more questions!
