Upgrading from Debian Lenny to Squeeze, those having this old embedded video card (my laptop is an IBM Thinkpad R40) have found their video performance dropped. This is due to debian’s policy which produced the distribution of this video card’s firmware in a package that is not installed by default with the x.org driver. In lspci -nn, the card is shown as

01:00.0 VGA compatible controller [0300]: ATI Technologies Inc Radeon Mobility M6 LY [1002:4c59]

After some browsing I’ve found out that this card is part of the R100 family, so the firmware you are searching for are contained in:

sudo apt-get install firmware-linux-nonfree

Make sure that /etc/X11/xorg.conf, if any, uses driver radeon or ati (which redirects to radeon). So in your xorg.conf there must be something like:

Section "Device"
        Identifier      "ATI"
        Driver          "ati"
EndSection

When you are done, you must restart Gnome (or whatever starts X):

sudo service gdm restart