I typed the line below and it shows me the correct diff:

svn diff file:///data/svn/webprojects/mediawiki/branches/1.5.3-osu file:///data/svn/webprojects/mediawiki/tags/mw-1.6.1 | less

when I typed: 
svn merge file:///data/svn/webprojects/mediawiki/branches/1.5.3-osu file:///data/svn/webprojects/mediawiki/tags/mw-1.6.1 

it sarted showing: 
D  maintenance/archives/.htaccess
and a whole bunch of other files deleted

I want to merge the difference between this tag and this branch into my local working directroy