Photoshop gets hampered by slower hard drives and lesser RAM whereas 3DS Max is an altogether entity.. It relies on almost all the major components for smooth and fast working.. So build a machine to run 3DS Max smooth and you wont need to worry about photoshop.. You'd definately need a quad core CPU ( LGA 1366 INTEL i7 preferably ) and 6 GB of RAM.. The next components are subjective.. Getting a SSD would surely decrease your load times by a huge margin but they are very expensive currently.. Also, choosing the GPU depends on the kind of work you do.. If you are a heavy texture and segments user, getting a fast quadro would really help you working smoothly in the viewport section.. Otherwise you could do with a consumer level card ( bang for the buck if you, even casually indulge in gaming on PC ).. I do use both of them at work and my current PC gets sluggish in handling heavy duty polygons in 3DS Max Design 2009..
My PC specs are :
CPU : Intel C2D E6750 2.66 GHz overclocked to 3.2 GHz
RAM : 4 GB DDR2 800 MHz CAS 4 Corsair DHX
GPU : Radeon HD 4870 1 GB
HDD : Hitachi 250 GB 7200 RPM SATA 2
LCD : 22 inches
OS : Windows Vista 32 Bit
Photoshop CS4 is fast enough although i've seen better loading times with a Seagate 7200.12 500 GB hard drive which my friend has