Welcome to G2G
Hope you don't mind if I pick that little lot apart a minute...
My main concern is the motherboard for the following reasons (some of which are down to personal preference admittedly!):
1) ECS are not one my favourite brands. This IS a personal preference I know but it's also based on experience
2) The CPU socket is 754 which is pretty much obsolete now
3) It uses DDR memory which also pretty much obsolete and is also quite a lot more expensive than DDR2
4) It has an SIS chipset. Again, personal preference but I'm really not a fan
5) It only has 2 memory slots (not the end of the world) but not ideal
6) It only supports SATA 150 which means your SATA 300 hard drive won't be supported at full speed.
For a few bucks more you could get an AMD 64X2 3800+ AM2 socket ($35.99) rather than a sempron.64X2 3800
If you want a decent motherboard on a tight budget, I'd recommend an Asrock such as the one below:Asrock Alive NF6P
or an MSI for example. Don't be tempted by a Jetway...
Although this will be more expensive you'll save some money be being able to buy DDR2 memory, rather than DDR.
I'd recommend Crucial, Kingston, Corsair, OCZ etc
Next MAJOR issue - I really won't advise you get that case with the 300W PSU. To start with, it's likely to be severely underpowered at 300W, secondly you really want a non-generic PSU.
Newegg do a range of cases that come without a PSU for under $25. I'd recommend you get one of those and buy a seperate PSU. The cheapest one that I'd recommend is this Antec 350W. At only 350W it's pushing it but if you're not planning on adding any extra hardware to the system then it should be fine:Antec
Failing that, for $30 you could get a Silverstone 400W PSU:Silverstone
The hard drive is fine but for an extra $6 you could get this Seagate which is the same speed but twice the size and comes with a 5 year warranty:Seagate
Hope this helps some