Try searching and reading this forum before posting.
You're doing nothing new that hasn't already been tackled.
In the future, use proper punctuation and occasional capital letters. It helps us follow your posts a bit better.
The power section will give you a few ideas to power your computer and some pros/cons of hooking your lcd to a socket vs psu. The LCD section will tell you why not to use a cheap lcd and also offer some power suggestions for the screen. Audio is a popular discussion in the general hardware section and your ghetto speaker approach has also been covered. linux vs win has been debated in the software section. Wireless internet was discussed in the general hardware section.
Use an expensive screen that supports VGA and touchscreen (eliminates the need for a seperate touch pad and text is crystal clear) such as Xenarc 700TSV. Mount it so that it looks stock in your dash, but doesn't require any permanent modification. If you were able to keep the stock stereo mounted, you could usee an adapter for cd in, tape in, or fm mod to get sound into the system. Otherwise, rewire the car to use a car amplifier. Don't rule out XP, 98, and lite editions OSes. Integrating with your wireless home network is easy via a wireless usb adapter (very kewl if you have a wireless campus or hot sites around town you frequently visit). For on the road internet, pick up cell phone with data plan and a usb link.
Good luck on your project.
Again, use the search button and read the plethora of previous posts. You'll find many of your questions already answered or even find things you never considered.