Dell Vostro 220s (Late 2008) - Manual (Page 61)

PCI and PCI Express Cards
61
See the documentation that came with the card for information on
configuring the card, making internal connections, or otherwise
customizing it for your computer.
CAUTION:
Some network adapters automatically start the computer when they
are connected to a network. To guard against electrical shock, be sure to unplug
your computer from its electrical outlet before installing any cards.
6 If you are installing a PCI Express card into the x16 card connector,
position the card so that the securing slot is aligned with the securing tab.
1 fully-seated card 2 not fully-seated card
3 bracket within slot 4 bracket caught outside of slot
1
2
4
3