FlyingHigh85 :
I believe the stock PSU is only 330W (AcBel pc9045-za1g). I'd like to run a 125-Watt Phenom II X4 or X6. It currently has a 65-Watt Athlon II X2 220. With the more powerful CPU, a discrete GPU, and 1-or-2-more HDDs, wouldn't I have to upgrade the PSU? Also, according to the ASUS site, the M4A78LT-M mobo has a PCIe 2.0 slot, but not a PCIe 3.0. Are the AMD and NVidia cards mentioned above compatible with my mobo?
I was looking at possible GPUs, and here are two:
$104 ZOTAC 2GB DDR3 NVIDIA GeForce GT 630 ZONE Edition VGA/DVI/HDMI pci-e Video
(http://www.newegg.com/Product/Product.aspx?Item=9SIA4UB20H2988)
$55 ASUS GT610-2GD3-CSM GeForce GT 610 2GB 64-Bit DDR3 PCI Express 2.0 x16 HDCP Ready Video Card
(http://www.newegg.com/Product/Product.aspx?Item=N82E16814121646)
Is the Zotac card worth the extra $? Why? I noticed both are passively-cooled. Would I be better-off with a fan-cooled GPU?
Yes, you will definitely have to upgrade your power supply, at least to a 550W to accommodate for two hard drives, a faster processor, and a discrete card. PCIe x16 3.0 is fully backwards compatible with PCIe x16 2.0, so you can use any PCIe x16 3.0 card, it will just perform at a lower level. If you plan to upgrade to a Phenom II X4 or X6, the graphics cards you are considering are very low end, entry level cards, being that they both use DDR3 memory, which is very slow, being the current generation of cards are DDR5. Secondly, these cards utilize a 64 bit memory interface, which is very slow, as the average interface of mid-range cards nowadays is 256 bits. If you are planning to use this for any gaming, you will hardly be able to run anything on more than low settings. It doesn't matter the amount of memory as much as the type and the interface. a 512 MB DDR5 256 bit card could easily outperform these cards with twice the FPS. Your CPU would be absolutely bottlenecked by any of these cards. To answer your other question, no, it would not be worth it to purchase the Zotac model. The difference is nominal, and they both will underperform. Passive cooling is a common feature on low end cards, and they tend to overheat when under heavy load. I would recommend the AMD R7 265. It has a 256 bit interface, utilizes DDR5, supports DirectX 11.2, and has 2 GB of memory, is completely compatible with your mobo, and will run well with a Phenom II X4 or X6. It also is only $60 more than the Zotac GT 610 you mentioned, with significantly better performance. If you add in 8 GB of RAM, a 550W power supply, and a Phenom II X4, you should be able to play most games on medium settings. Good luck!
A word of advice: Phenom II processors are no longer sold retail and can only be bought used through sites such as ebay. The best one for the money is probably the Phenom II X4 965 Black Edition. it goes for around $100, and is still a fast processor.