When boxers are pregnant, can you still take them out for walks?

Yes! In fact it is vital that any pregnant bitch is exercised or she will not be able to whelp her puppies. My bitches always get their normal exercise as soon as they're out of season until about 5 or 6 weeks of pregnancy, when they naturally start slowing down. Let her dictate how much exercise she gets. Obviously don't overtire her, and in the later stages don't let her jump up onto things (she may not be able to even manage the stairs), but several short walks a day are a very good idea, even up to the day of whelping.
:)