The SVN repository is public and everyone has read access. The repository uses a standard SVN layout of:
xerces/c/ | | - branches/ | | - tags/ \ - trunk/
In short:
1) to check out the trunk of xerces/c:
svn co https://svn.apache.org/repos/asf/xerces/c/trunk
2) to check out the code tagged with the Xerces-C_2_4_0 tag:
svn co https://svn.apache.org/repos/asf/xerces/c/tags/Xerces-C_2_4_0/
3) to check out the code in the peiyongz/ branch:
svn co https://svn.apache.org/repos/asf/xerces/c/branches/peiyongz/