Are you sure he's going to do CAD using Photoshop?
Anyways, for general graphics/CAD the system requirements are similar, so here goes, (assuming a flexible budget)
Intel Core 2 Q6600
Gigabyte GA-X38-DQ6 motherboard
Corsair/Transcend/Kingston 4 GB DDR2 RAM (Suggestion: Corsair - 4-5-5-15 or...