permissions to update a directory

Hi all,
Why is it that when I update a directory in a working copy, I need to have
the rights for all the "brothers" directories?
eg :
workcopy/dir1
workcopy/dir2

'svn up workcopy/dir1'
-> svn up failed : you do not have permissions to write in
workcopy/dir2/.svn/***

I only want to update the content of workcopy/dir1, no matter what there
is in dir2.
Is this something I can do to bypass this restriction?
thanx in advance

-- 
Erwan Lacoste
Stagiaire
RHAPSO
1, rue Galvani
91300 Massy
Tel +33 (0)1 60 13 79 50
Fax +33 (0)1 69 32 19 61
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