write-permission for temp/cache - i allready did that

I have used (earlier versions of) SPIP before and liked it at lot.

I am now setting up a new website and installing SPIP. That is - I try to install SPIP. Because in the installation process I am told, that

The following directories do not have write permission :
* tmp/cache/

...but they do !

I have set both of those directories (’tmp’ and ’cache’ in ’tmp’) to 0777 - write-access for everybody.

So now I cannot move on and I dont know how to go on.
Please help.