Biggest bottleneck I see is the hard drive. But that's typical for most systems. However your is a green drive, which is more focussed on saving energy.
I suggest you check out an SSD, preferrably from OCZ or Intel. I like the Vertex II 100 or 120 GB in the $200 range.
If you are absolutely opposed to the idea, then there is a samsung 2TB on newegg that is here for $80:http://www.newegg.com/Product/Product.aspx?Item=N82E16822152245