Buy a new PC or update existing one?

Hey everyone,

My old desktop is sitting idle since I've migrated to using a laptop almost exclusively but I'd still like to see if I should buy a new one or update it if possible. I'd like to use the desktop for general work, internet and somewhat heavy Adobe Photoshop graphical work.

The current desktop specs:

Case: Elite 335 (RC-335) Cooler Master

Motherboard: Asus M3N78-VM

CPU: AMD Athlon II X4 620

Video card: ATI Radeon HD 4600

Memory: 4GB RAM (2 x Kingston 2GB DDR2 RAM 800MHz PC2-6400 240-Pin DIMM)

Primary HDD: WD 250GB 7200 RPM 8MB Cache SATA 3.0Gb/s

Secondary HDD: Maxtor 500GB 7200 RPM 16MB Cache SATA 3.0Gb/s

Windows 7 32-Bit

Would it be more cost efficient to buy a new one or try updating it?

If so, suggestions for a new desktop model or specific hardware to update would be appreciated. I'd like to use Windows 64-bit in any event.

Cheers...