AVR Freaks

TFT displays need a datastream of usually three 6-bit pixel values (r,g,b) at a rate of the order of 35-40MHz. Plus clock & 3 sync signals (HS,VS,Data enable)
Supply and logic levels are usually 3.3v (plus the HV supply for the backlight)
This is beyond the capabilities of the AVR to drive direct, but is relatively easy from a small CPLD of FPGA, which can either update the display from an attached RAM chip, or make patterns etc by 'on-the-fly' generation of data based on X/Y address counters.
You may just be able to get some pretty patterns out of an AVR by driving at a low frame rate but you'll be pretty limited as to what you can do.
A complication is that later panels multiplex the 18 bit pixel data, sync and clocks into 4 high-speed LVDS channels. However panels of the 800x600 era tend to use a discrete LVDS receiver chip, so you can either use the corresponding transmitter chip, or take the receiver chip off and feed in the parallel data direct.

Here is some data on your panel :
http://support.advantech.com.tw/Cservice/LCD.nsf/f99b88c84af1eeff482565ec000759ea/e86ed64623eeeafd482568a800285ea8?OpenDocument

There is some info and links to some TFT panel data near the bottom of my page at www.electricstuff.co.uk/ektapro....
Specs of similar-sized panels are generally similar - for a given panel size, the main difference is whether the interface is LVDS or Parallel (latter often termed TTL), and sometimes some minor differences in sync timing, so you can often use the datasheet of a similar device to get going, as datasheets can be hard to find.
Don't run the panel for extended perions without clock or sync as this will cause electrolytic damage.