I posted this in a request topic, but this is good it has it's own place now. Here are the dimensions:
The resolution should be 300 dpi. Here are some dimensions for you:
Standard Cases
Single Amaray = 3240 x 2175 (170 spine)
Double Amaray = 3305 x 2175 (235 spine)
Triple Amaray = 3384 x 2175 (314 spine)
4-5 Disk Alpha = 3508 x 2175 (438 spine)
6-7 Disk Alpha = 3661 x 2175 (591 spine)
Blu Ray / HD-DVD = 3118x1748 (140 spine)
Slim Cases
ThinPak Single = 3150 x 2175 (80 spine)
ThinPak Double = 3180 x 2175 (110 spine)
Slimcase 3-4 = 3240 x 2175 (170 spine)
Slimcase 5-6 = 3370 x 2175 (300 spine)
Slimcase 8 = 3395 X 2175 (325 spine)
Slimcase 10 = 3460 X 2175 (390 spine)
Other
Label = Min : 1400 x 1400 Max : 1600 x 1600 (1500 x 1500 is standard)
DVD Insert = 1450 x 2150
note that most regular width (170 spine) are available for multi disc cases, so if you have a 2- 3- or 4- disc case, you dont need the wider spines, the single width will work just fine.