I have it installed on my SME 8 server, but don't remember the exact steps.
I think I did this (at least, I just successfully upgraded ioncube from 4.0.10 to 4.2.2 using this procedure):
1) create ~/addons (a place for downloaded addon software) and cd into it
2) download the latest iinux x86 .zip file from
http://www.ioncube.com/loaders.php (right-click; copy link; switch to command window; wget <paste>)
3) unzip the downloaded file
4) copy the contents of the unzipped file to /usr/lib/php/modules
5) Create
/etc/e-smith/templates-custom/etc/php.ini/15ioncube containing:
zend_extension = /usr/lib/php/modules/ioncube_loader_lin_5.3.so
magic_quotes_gpc = off
6) restart httpd-e-smith using
sv t httpd-e-smith