Duda sobre las RAM y placa base

Hace un tiempo que tengo una duda repsecto a las placas base y las memorias RAM, os expongo un caso:

Demos la situación que yo me quiero comprar esta placa base:
ASUS Crosshair III Formula - Socket AM3 - Chipset 790FX - ATX
*•AMD AM3 CPU support
•AMD 790FX/SB750
•DDR3 1600(O.C.)
•MemOK!
•CPU Level Up
•SupremeFX X-Fi

CPU AMD Socket AM3 ;Phenom™II /Athlon™II /Sempron™ 100 Series Processors
AMD 140W CPU Support
AMD Cool ´n´ Quiet™ Technology
Supports 45nm CPU
Chipset AMD 790FX/SB750
System Bus Up to 5200 MT/s ; HyperTransport™ 3.0
Memory 4 x DIMM, Max. 16 GB, DDR3 1600(O.C.)/1333/1066 ECC,Non-ECC,Un-buffered Memory
Dual Channel memory architecture
*Refer to www.asus.com or user manual for the Memory QVL (Qualified Vendors Lists)
**Due to OS limitation, when installing total memory of 4GB capacity or more, Windows® 32-bit operation system may only recognize less than 3GB. Hence, a total installed memory of less than 3GB is recommended.
Expansion Slots 2 x PCIe 2.0 x16 (@ dual x16)
3 x PCIe 2.0 x1 ( the PCIEx1_1 (black) is compatible with audio slot)
1 x PCI 2.2
Multi-GPU Support Support ATI CrossFire™X Technology graphics cards
Storage SB750 Chipset
1 xUltraDMA 133/100/66 for up to 2 PATA devices
5 xSATA 3 Gb/s ports Support RAID 0,1,5,10,JBOD
1 x External SATA 3Gb/s port on rear (SATA On-the-Go)

• Due to the Windows 7/XP/ Vista limitation, the RAID array with the total capacity over 2TB cannot be set as a boot disk. A RAID array over 2TB can only be set as a data disk only.
  LAN Gigabit LAN controller, featuring AI NET 2
  Audio SupremeFX X-Fi Audio Card
  8 -Channel High Definition Audio CODEC
• EAX® Advanced™ HD 4.0
• X-Fi CMSS®-3D
• X-Fi Crystalizer™
• Creative ALchemy
• Supports 1 x S/PDIF out header
• Supports Coaxial/Optical S/PDIF out ports on rear
  IEEE 1394 2 x 1394a ports (1 port at back I/O, 1 port onboard)
  USB 12 USB 2.0 ports (6 ports at mid-board, 6 ports at back panel)
  Overclocking Features MemOK!
  CPU Level Up
  Extreme Tweaker
  Power Design:
• 8+2 phase CPU power design
  Keyboard-TweakIt
  iROG
  Loadline Calibration
  Intelligent overclocking tools:
• ASUS TurboV
• O.C Profile
  Overclocking Protection:
• COP EX (Component Overheat Protection - EX)
• Voltiminder LED
• ASUS C.P.R.(CPU Parameter Recall)
  Special Features ASUS MyLogo 3
  ASUS EZ Flash 2
  ASUS CrashFree BIOS 3
  Q-Connector
  ASUS Q-Fan 2
  External LCD Poster
  ASUS Q-Shield
  AMD® OverDrive Support*
  ASUS TurboV
  Back Panel I/O Ports 1 x External SATA
  1 x IEEE 1394a
  1 x LAN(RJ45) port
  6 x USB 2.0/1.1
  1 x Clr CMOS switch
  1 x PS/2 Keyboard port(purple)
  Internal I/O Connectors 3 x USB connectors supports additional 6 USB 2.0 ports
  1 x IEEE 1394a connector
  1 x IDE connector for two devices
  3 x thermal sensor connector
  5 x SATA connectors (Blue)
  System Panel connector
  8 x Fan connectors: 1 x CPU / 1 x PWR / 3 x Chassis / 3 x Optional
  1 x LCD Poster connector
  24-pin ATX Power connector
  8-pin ATX 12V Power connector
  BIOS 16 Mb Flash ROM
  AMI BIOS, PnP, DMI2.0, WfM2.0, SM BIOS 2.4, ACPI2.0a Multi-Language BIOS
  Manageability WOL by PME,WOR by PME,PXE
  Accessories SupremeFX X-Fi audio card
  1 x 2 in 1 Q-connector (USB, System panel; Retail version only)
  1 x Multi-functional module (1-port IEEE 1394a + 2-port USB2.0)
  External LCD Poster
  UltraDMA 133/100/66 cable
  Serial ATA cables
  I/O shield
  Cable Ties
  User´s manual
  Support Disc Drivers
  ASUS PC Probe II
  ASUS AI Suite
  ASUS Update
  Kaspersky® Anti-Virus
  AMD OverDrive Utility (AOD)
  Sound Blaster X-Fi Utility
  Futuremark® 3DMark® 06 Advanced Edition
  Form Factor ATX Form Factor
  12 inch x 9.6 inch ( 30.5 cm x 24.5 cm ) *
  Y por lo tanto que yo uso intel y la placa es AMD pues me deberia cambiar el procesador, en el caso demos la situación que me decanto por este:
  **AMD Phenom II 955 X4 Quad Core 3.2Ghz Black Edition AM3 Box **

Entonces digamos que a mi con la compra de estas dos piezas no me queda más dinero, pues me vería obligado a o no usar el PC o simplemente meter las DDR2 en una placa base AM3, eso sería posible?
Es decir, formulo la pregunta de otro modo, puedo meter RAMs DDR2 en una placa base DDR3 o AM3?

O simplemente dan esa información de la placa porque es lo recomendable pero cabría la posibilidad de poner cualquier RAM DDR2 y que el pc funcionase?

Espero que las repsuestas no sean del palo, pues comprate unas DDR3, no porfavor.

Gracias a las posibles respuestas.