|"im using nvidia geforce 7200 gs for graphics"|
NVidia has already been thru the 7000, 8000, & 9000 series & has moved on to a whole new model/numbering system. The 7200 is at least 3 generations old plus it never was a good card to begin. It's the slowest card in the 7000 series & was introduced as a low cost/low end replacement for onboard graphics.
"i have no onboard video card"
Then your board must be revision 2.0 which is based on a different chipset & has 4 memory slots, Would this be your board?
"I have read some about the FSB speeds"
AMD systems don't use a FSB. It was replaced by the HyperTransport bus many years ago. Some sites still refer to it as FSB, but that's totally incorrect. The FSB is considered to be the communication path between the CPU & memory controller. Up until AMD introduced the A64, the memory controller was part of the motherboard.chipset & the FSB speed varied depending on the CPU frequency (100MHz, 133MHz, 166MHz, 200MHz, etc). The A64 has the memory controller right on the CPU die & they communicate with each other at full processor speed, thus eliminating the FSB altogether.
The HyperTransport bus is the communication path between the CPU & motherboard. It is the product of the CPU reference clock & HT multiplier. All AMD CPUs since the dawn of the 1st A64 run with a reference clock of 200MHz. Your board uses the 1st revision of HyperTransport, HT 1.0, which runs at 1000MHz (200MHz x 5), but since it's a bi-directional bus, it's said to run at 2000MHz aka 2000MT/s (mega transfers per sec).
Your AM3 CPU was designed for HT 3.0 which runs at 2600MHz (5200MT/s), so by running it in an HT 1.0 board, you're taking a performance hit.
"which is better using both dimms 2gb on 667 or only 1 gb on 800mhz"
Ideally, you should be running all DDR2-800 RAM, but 2GB at 667MHz is better than 1GB at 800MHz.