First I need more info about the two computers.
1) What type of RAM do each have?
2) What are the HDD that the computers have?
Second, the graphics card on the desktop is better than the one in the laptop.
1) I believe the Dell has PC5200 Ram. (DDR2, 4GB) and the laptop has DDR3 2GB Ram. (Not sure what type)
2) The laptop has a 250GB HDD Sata 7200 RPM, and the desktop has a 500GB Sata 7200 RPM.