Your desktop's setup options should have a DPI option somewhere. In Gnome 2.x, it's System > Preferences > Appearance > Fonts > Details > Resolution (DPI).
If you are using LXDE then you can set the DPI from the command line as follows (you can put this in a shell script and set it to run on startup):
echo "Xft.dpi: 160" | xrdb + - if killall -w -u $(whoami) lxpanel pcmanfm; then lxpanel & pcmanfm --desktop --profile LXDE & openbox --replace & fiYou may wish to run obconf and set Openbox to put the Maximize button on the left, so it is more easily reachable when a window sizes itself larger than the screen and you want to bring it back to screen size.
For a larger mouse cursor in LXDE, try the crystal-cursors or crystalcursors package (you might need to select it in the "Appearance" or "Customise Look and Feel" settings). Also try qtconfig in qt4-qtconfig for setting the font size of Qt applications.