Depends. Your prelude takes 9006 bulbs, and the 240sx hatch (wtf sileighty?!) would need a H4 conversion. If it's truely got the silvia front end, the triple projectors use H1 bulbs, and dual projectors use H3c - in which case I've never seen a HID H3c.
And I obviously know enough about lights...
For kits, Ebay and other online places sell them. www.hidplanet.com has retrofitting and other HID information.
-Jeff