You can start by browsing boards or processors.
Assuning you know what processor you want (say Core 2 Duo?), i would go to the support page http://www.intel.com/p/en_US/support?iid=hdrgg-US+support
and select processors -- desktop -- Core 2 Duo -- View product support page.
This page gives you a ton of information on the processors including a link under Resources & Utilities to the Intel® processor and boards compatibility tool
This nifty little tool will let you search for Intel Boards that are compatable which what ever processor you would like to use.
My random choice here was a Core2 Duo E7600
The reslut is a list of 30 boards that can support this processor.
Chosing the high end board DX48BT2 since I am a high end kind of guy.
This takes me to the board product page where you will find a TPS (Technical Product Specification) which tells you way more than most folks ever want to know about a system.
There are also posted Tested Hardware, Tested memory and Tested processor lists to let you know which components will play well with each other.
The Intregration guide are also listed on this page.
Starting with the memory is a bit toughter, but a general seach of Http:\\www.Intel.com will get you started finding a board for this older memory.
(Sorry, most of the newer processors need DDR3 memory)