Any of the P35, P45, X38 or X48 chipset boards will run a Q6600
SLi is Nvidia cards in a multi card configuration, Crossfire is AMD/ATi cards in a multi card configuration, i.e. more than one video card
DDR2 is the older standard for memory, DDR3 is the newer faster/larger capacity standard for memory.
EDIT: I looked at your link, nvidia chipsets (as opposed to the Intel ones I listed above) are required for multi nvidia card setups (SLi) unless you go to the new X58 chipset which some boards offer both SLi and Crossfire support on the same board, otherwise it is Crossfire for AMD/ATi cards only and SLi for nvidia cards only, i.e. you can't run nvidia cards in Crossfire of AMD/ATi cards in SLi.
You can however run single nvidia cards on Crossfire boards and I'm pretty sure you can run single AMD/ATi cards on SLi boards.