Ok several things to note in your thread from a building/upgrading POV.
Firstly the computer you have listed has a reasonable CPU and ok motherboard, nothing to write home about but since you're looking @ $300 PCs, I'm assuming that you're operating on a sub $500 budget or less. This means that you're not going to be getting a
good gaming PC... you can get a PC that
can play games, but it's not going to be good at it

The computer in your second tigerdirect link (amd vision) has a graphics card but it is a 5450 which is like a couple of steps above no discrete graphics at all.
Now if you're looking to pay minimal $$ now and put higher end components in later when you can afford them, I'd suggest looking at barebones with:
- Decent AMD motherboard (& low-mid range processor)
- Decent PSU [like a VX450]
- 2-4 GB of ram (1333mhz ddr3 - no point to higher freq ram with your budget)
- A case with at least 1x 120mm intake & 1x120mm exhaust, enough space for mid range graphics cards
- A smallish 7200rpm drive (500gb spinpoint F1?)
- A very cheap GPU or motherboard IGP so that you can save up for a
decent graphics card later.
Finally... and this is very important...
Graphics card's performance levels are not determined by how many MB of memory they have on them. Do not be fooled into thinking that just because 1 graphics card has 1024MB of VRAM that it is better than a 512MB variant... because that's not how it works.
To figure out how decent the cards are, you type their name into google with 'review' after it, and read a few of the articles. For example with your one:
hd5450 review - Google Search
And then one that I would recommend to you for budget gaming
hd5770 review - Google Search
Then you look for games that have been tested on both cards and compare them.
The 5450 vs 5770 on Crysis medium quality:
7 fps vs
38 fps