It's called a network adapter. Buy the new one for slim PS2s. It will probably run ya 20-25 USD. Here are 5 games to buy(If you can play M-rated, that is...:
1. Resident Evil 4
2. Devil May Cry 1 and 3 (Special Editon version)
3. Metal Gear Solid 3: Subsistence
4. Red Dead Revolver
5. Mercenaries
6. All Timesplitters
7. GUN
8. All GTAs(never played em though not allowed >.< )
9. SSX On Tour
10. Ratchet and Clank: UYA/Jaws/Indigo Prophecy/any Spiderman/WWE: S vs. R '06, etc.!
I got Scorpion King and Rally Fusion: ROC w/ mine!
CYA!