AutoCAD LT 2008 slow performance problems

Hi everyone, first of all, I'm sorry for my English.
My hardware configuration is: Lenovo T61P, Intel T7700@2.4GHz, 4GB
Ram, Nvidia Quadro FX570M (1920x1200), HDD 7200 rpm, Win XP pro, AutoCAD LT 2008 SP1.
I'm experiencing the following issue: 1) I import an Xref or a block that contain a HATCH 2) I select the Xref or the block to move it 3) My graphic card slows down to refresh the HATCH when i move or pan the selection.
Better but still bad performance results when the object is zoomed out and fills only a small part of the screen... but in this way it is impossible to find the right point to move the selection.
No such problems on the same drawings with AutoCAD full installed on older (and slower) PC.
Any suggestions? Thank you very much.
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