In the option box there is a PCI-X riser card
like the one shown here:
Unplug the riser card from the Altos R520
and identify the Full Height Riser card
All the How To guides can be found on http://support.acer-euro.com/documents/howto/
SO.R51PC.I01 - R520 PCI-X Full Height Riser, 1x PCI-X 133MHz slot
How To add the R520 PCI-X Riser card
Shift the card like in the picture to unlock
and remove the card.
Plug the new PCI-X card and shift it to lock.
Pull the plastic hook like it is shown in
The riser card is ready to be installed.