PCMCIA to 4USB is a necessity for one of the PCMCIA's
Costs about 10$
Here are your options
1. you MUST get a SSD. No way is a HDD gonna last in a simple thinkpad without proper suspension (like in a toughbook) Depending on size: a few hundred $
2. Get a GPS and Delorme, and have the ultimate GPS unit, some software i think lets you do that with your TP too. About 65$ for a full kit [that's a USB btw]
3. If you intend to use it as a media center unit, then buy a PCMCIA MCE remote system, that lets you change the music and etc by remote. I wouldnt suggest it be a movie player for obvious reasons, this is about 10$
Don't forget to a car adapter/inverter (at least 100-200 watts) if you don't have one already. close to 50$ depending on quality
4. Depending on your resources, you can get a Line-in cable to your car's audio system to boost the power of any music or audio you want [Surround sound Turn-by-turn directionality anyone?]
If you need a stereo adapter for this, that will run a few hundred unfortuantly
. But then you don't need any crappy Laptop speakers!
P.S. If you want to save on SSD costs, download orb and keep it all on your PC and just connect via your TP's Data.
Also, for the second PCMCIA, get a WiFi, you won't regret to have a WiFi
A good mic (for text to speech)
If you get a camera for your dash, you can transmit the audio digitally to your PC"s storage.
Lots of opprotunity! Good Luck! Remember to find something to give it a good mount to the car, and that SSD or some sort of suspenison for the drive