Vista 64 bit, fonts and some games

I run a computer with a 30" Dell monitor, using an Nvidia 8800GTX card &
latest drivers, 4 gb ram and Vista Ultimate 64 bit. If I run Vista at a
desktop resolution of 2460 x 1600 (the native resolution of the monitor) I
find the fonts generally to be too small so I go to Control Panel -
Personalization, Personalize appearance and sound, Adjust font size (DPI)
and adjust the DPI setting to 150%. Everything is cool. However, if I try to
go higher, to, say 200%, then I find that many games won't work properly.
For example, World of Warcraft gets to the start up screen but the font
cursor remains stuck in the center of the screen, for Assassin's Creed it
gets by the initial publishers, etc. splash screens and then goes black
while the sound continues normally. If I change the DPI setting back to
150%, the games then run properly.

Now, my questions are: Why is this happening? How do I correct it? In other
words, how can I get Vista to run the DPI at 200% and still get the games to
work properly? Thanks in advance.