Wait have you already got this build, if so then its ok.... like 8/10
The Seagate is good depending on the one. If it is the 7200.12 then its a pretty decent HDD. Don't get the Crucial SSDs WAY overpriced.
Get the Vertex 2 or wait for the Vertex 3 (SF-2000 controller with SATA III) Better than the C300 by a long shot and a better controller. The V2 loses to the C300 by a little bit in reads, but OWNS it in writes. (not OWNS but you get my drift)
As for if you havent bought it those parts are outdated and all those stuff are dirt cheap now (RAM, PSU etc etc).http://www.squidoo.com/electronicandmore
Refer to that guide, PSU change it to the XFX 850 to save money.