With the last Ubuntu Lucid 10.04 come a new graphical module: KMS or Kernel-based Mode-Setting.
If you have performance problems in some games like Quake 3 or TCE / Enemy Territory, try to disable KMS.
The problem can also be with the mouse pointer (slowness, lag, delay or inacuracy).
/etc/default/grub then issue the command
vi /etc/default/grub GRUB_CMDLINE_LINUX="nomodeset" update-grub
nomodeset at the end of the
# kopt line, then issue command
vi /boot/grub/menu.lst # kopt=root=/dev/sda1 ro nomodeset update-grub