The new MSI X48 Series motherboard supports the latest 45nm multi-core Intel processors & XMP (Extreme Memory Profiles) with up to FSB 1600 & DDR3-1600 to bring the most powerful performance. The FSB 1600 support will prepare the fully compatible with the highest segment of Intel 45nm quad-core (Yorkfield) processors, and XMP also provides a direct way to boost the high speed memory module up to 1600MHz (even more) and gives extreme performance to the enthusiast.Both motherboards support Intel's latest processors and the difference between the two boards is that the X48C Platinum has support for DDR2 and DDR3 memory. This is nice for people who want to use their old memory instead of shelving out tons of money for DDR3 memory but I'm a bit skeptic as most DDR2/DDR3 motherboards don't really perform that well. Another big difference between the two boards is that the X48 Platinum has 4 PCI Express slots for ATI CrossFire, two slots run at x16 and two at x4. The X48C Platinum only has two PCI Express x16 slots.
Another minor difference is that the X48 Platinum has Dual Gigabit LAN while the X48C Platinum only has one Gigabit LAN port.
Source: VR Zone