Will the parts works together? Yes, but I ask that you keep a few things in mind before making this a final list.
1. Yes, you can use Windows 7 OEM. The differences between the OEM and retail versions are mostly related to the license. Microsoft defines a PC based on the motherboard. The OEM version is paired to your motherboard, if you get a new mobo, you need a new license, however, there is nothing technically preventing you from just simply reinstalling all over again. Retail licenses can be moved between PC's, but never installed on more than one at a time.
2. I'm reluctant to suggest that motherboard and CPU combo for a gaming rig. The motherboard uses an older AMD 7xx series chipset, but the 8xx series is out now. This new series allows for SATA 6 and USB 3.0, which will be helpful for future upgrades. The ASRock 870 EXTREME3 AM3 AMD 870 SATA 6Gb/s USB 3.0 ATX AMD Motherboard
is the 8xx series equivalent to the AMD 770 chipset. If you're playing older games designed with dual, not quad, core CPU's in mind, that CPU will be fine, but if you are playing higher-end games that really push the CPU, a quad is suggested. The AMD Athlon II X4 635 Propus 2.9GHz
is a good alternative. However, the Phenom II line has better performance than a similarly clocked Athlon II. For the Phenom II, the AMD Phenom II X4 945 Deneb 3.0GHz
is a lower-cost alternative, for a Phenom II, that should run well.
3. 64-bit Windows is best used on a PC with 4GB or more of RAM though it can be installed and ran on systems with reduced amounts of memory. Keep in mind that items in memory on a 64-bit system take up slightly more space, which isn't an issue on systems with 4GB or more of RAM.
4. With the GPU, you are pretty much limited to AMD/ATI GPU's if you want to Crossfire. A solid mid-range graphics card is the ASUS CuCore Series EAH5770 CuCore
since it offers excellent performance vs. price.