So it seems we're stumped here.
You have a Lenovo T400 with P8600 2.4 Gz Processor, 1440x900 display, GMA 4500 MHD Intel GPU.
Windows 7 preinstalled
Fresh install of Fedora14 that did not boot into the graphical environment during the first reboot after install.
You were able to edit grub to load the vesa driver to get into a graphical environment.
You used the display config GUI to create a custom xorg.conf
How do you access the Fedora disk to retrieve the log data after X crashes? Do you boot from the install disc and mount the sysimage?
Have you looked through the link I sent you to the thinkwiki where there were a number of posts describing various issues with IBM / Lenovo hardware?
Get a liveCD image and boot from that. Then visit the log files to see what is happening.
Boot into Win7 and check the event log for any warnings or red flags.
I see the the Laptops running Fedora thread a T400 and T500 listed, both did not indicate any graphics problems. It may be that you have a memory problem that shows up in Fedora because of the way linux maps memory that doesn't show up in windows. You might want to run memtest. It looks like it is a problem specific to your machine since I have not found another post on this forum that describes the same symptoms for this Intel GPU.