Well Tim, welcome to the world of boxers. I got my first boxer in March of this year. She's going on 10 mos now. Well, at 7 weeks old, she constantly peed, pooped, you name it, whenever in her crate. My husband and I would take her out and let her do both before we left, and if we came back half an hour later, 3 hours later, didn't matter, she went in the crate again! One word of advice, do not leave food and water in their crates. Make sure they have ample opportunity to eat and drink when you're home, but never give them added ammunition when alone in the crate.
I have found from listening to others on this board, that this seems to be somewhat common among the breed. They do outgrow it quickly though. It seems like an eternity to those of us cleaning it up.

It basically takes them longer to mature, so at 7 weeks old, they really aren't there yet. Within one week, Zoe stopped pooping in the crate, but it took another 3-4 weeks to stop the peeing. The grossest part is how they will lay in it and not even care!
If the crate seems at all too big, try petitioning it off, but I think you're just going to have to wait for a little more maturity. We even asked two separate vets about the problem, they had no answers for us. I think it's just part of the entire separation from mom and siblings, new surroundings, new routines, etc. It really helps to get them house broken ASAP, this stopped our problems immediately. One of the best ways to do that, reward EVERY time with treats. Every time she goes poop outside when you ask (use trigger words like, poo poo, every time you take her out and ask her to go) give her a treat right away with lots of praise. Once we tried this (we weren't fond of treat training, we don't do this with our other dogs), it only took about 2 weeks to fully house break Zoe.
Good luck, hopefully others on here will have more advice for you. I know we had to wait it out, but it seems like a distant past now, Zoe is absolutely wonderful and we wouldn't trade her for anything in the world. Just figure on taking the kennel out for a good hosing each day.

Jessica
------------------------------
Zoe-1/16/00, plain fawn, cropped, spayed, docked
Jake-2/3/98, yellow lab