I have a Dell Inspiron 510m with Intel 855 graphics and I get the same problem if I have 3d desktop effects like Beryl etc turned on. It is the same whether it is PCLinuxOS, Ubuntu or Mint. Do you have desktop effects turned on? Maybe that is part of the problem??
If there is a solution or an explanation I would also be interested in hearing it.
BTW Linux Mint is brilliant. I probably won't go back to PCLOS on this laptop - Cassandra is just too pretty and so damn good to use.
Thanks to the whole Mint team.