I don't think SVN has that functionality built in, but if you are able to run commands on the server that holds the SVN repository (and assuming the server has the standard UNIX/Linux tools available), this bash script should do it for you:
REPOS=/path/to/repos
FILE=dir/foo.xml
for rev in "$(svnlook history $REPOS $FILE | awk 'NR > 2 { print $1 }')"; do
rev_date=$(svnlook date -r $rev $REPOS | awk '{ print $1 }')
svnlook cat -r $rev $REPOS $FILE > ${rev_date}_${FILE}
done
This will produce filenames of the form 2007-08-08_foo.xml. Of course, you have to change /path/to/repos in the first line to the actual filesystem path (not a URL) of the repository, and dir/foo.xml in the second line to the path of the file within the repository.
If it's really important to you to have underscores in the date, change line 4 as follows:
rev_date=$(svnlook date -r $rev $REPOS | awk '{ print $1 }' | tr - _)
Also keep in mind that if the file was ever modified more than once on a given day, only the first edit on each day will actually be reflected in the written files.