Do i need the old version of sims2 to play sims2 pets?

It depends. If you're getting the game for the PS2 then no you don't need the original Sims 2. On the other hand, if your getting the PC version then yes you do need the original copy of Sims 2.

They put all the information on the disc for the PS2 and all the information is loaded off that. The PS2 has no internal hard drive so it can't save games to it. When an expansion might come out for the PC version they need to make a whole new game for the PS2 version.

The PC version is an expansion pack. Its basically more stuff that the developers added to the game since its release. Since you already have the core data needed for the game they just release the extra data needed for the expansion. When you install and run the expansion it takes information from the original game and the expansion.

yes, sims 2 pets is an expansion, thus you need the original game to play

you need "sims 2", but not all of the expansion packs, such as "sims 2 glamour life".

yes u do