play your ipod through the speakers of your car...where can i buy the adapter thing and what's it called?

Those are called iPod FM Transmitters for cars.  One choice is the Griffin iTrip Auto Transmitter selling for $24.99 on Amazon!
specifics:

• Combines a powerful FM transmitter with an integrated charger in order to recharge your iPod
• Transmits clear music through your car stereo
• Features selectable LX and DX modes for best-quality audio under real-world conditions
• Can operate anywhere from the 88.1 to 107.9 MHz frequencies; range of 10 to 30 feet
• Compatibility: iPod nano 1G, 2G, 3G; iPod mini; iPod 3G, 4G, 5G, 5.5G, 6G

There is also the Belkin Tunecast that sells for $37.72
specifics:

• ClearScan one-push station locator
• PRO setting optimizes audio and boosts volume
• 2 programmable preset buttons
• High-contrast backlit display
• Car charger

There is also the Ez Blast which sells for $25.99
specifics:

• LCD Screen
• Crystal Clear Sound
• Easy to Use Power and Station Selection Buttons
• Charges Your iPod during Use
• Transmits On All Frequencies from 87.7 to 107.9