LCDs are not like CRTs. An LCD that has 1280X800 resolution has 1280 columns and 800 rows of red, green and blue LCDs. There are 2 screen resolutions on the T400. You bought the WXGA one. The motherboard is not the limitation.
I do not respond to requests for private, one-on-one help. Your questions should be posted in the appropriate forum where they may help others as well.