How to Downgrade back to 0.8.6 ASAP

[turbanator]

so I upgrasde from 0.8.6 to 0.9.0 and it doesn't work due to me still running php 5.2.x.  I can't upgrade or do a dual php install at the moment. 
Can someone explain to me how to downgrade back to 0.8.6 please ASAP? 

running Debian Lenny.
PHP 5.2.6-1+lenny16 with Suhosin-Patch

[SKaero]

Replace the 0.9 files with the 0.8.6 files. If you already updated the database you'll also need to restore that from a backup.