AM2 boards and AM3 CPU

so is it true that AM2 boards and AM3 CPUs will work together? If i buy a AM2 board and AMD Athlon 64 CPU, how long will I be in the somewhat of current technology? and SATA-2 hard drives controllers work with the original SATA-1 (the first generation of SATA produced)? I have found on tigerdirect the computer parts I wish to buy for a brand new 64-bit computer. The total would be about $400 for this computer with a Gigabyte M51GM-S2G mATX motherboard. do you think i am getting the a good board??