You do unit tests, that's good.
You do weekly builds, that's not so good.
XP is about building the software several times a day using automated software like CruiseControl. If you build only once a week, it means you are checking-in only once a week, and problems found after the build are solved during the whole next week.
It is not agile to do things like that, you need to check-in daily, even if you just changed a method, if it passes all the tests, check it in. CruiseControl will verify that your check-in is safe a few minutes after you checked-in that code.
Solving build breaks is the responsability of the committer. Usually build breaks are published on a web site, which means every developer has a reputation at risk, and they are TOLD that build breaks are priority 1, so they solve build breaks (or test breaks) a few minutes after they are produced. IMHO, that's the basis of being agile.