Budget build (600-700$)

Approximate Purchase Date: Pretty soon

Budget Range: 600-700$ without rebates, kind of skeptical about them.

System Usage from Most to Least Important: engineering work, browsing, movies, light games if possible.

Parts Not Required: All parts are required, i could get a 1TB WD Green hard drive though.

Preferred Website(s) for Parts: newegg/amazon/microcenter

Country: Columbus,OH,US.

Parts Preferences: Good Full HD monitor (23-24" preferred), Micro ATX Preferred. Front USB 3.0. AMD graphics and Intel/AMD CPU

Overclocking: Maybe if build allows for it.

SLI or Crossfire: No

Monitor Resolution: 1920x1080

Additional Comments: Needs to be good enough to help me get my work done (coding and computation) and be a source for my entertainment as well. Quad core is helpful (Coming of a core i5 750 and HD 5850).

I have a 2008 Core 2 Duo Macbook 2.0 Ghz 8GB Ram, should i just go ahead and get an external monitor for it ? Will it lag for normal browsing coding etc (I notice lag in Cnet website itself when scrolling) ?

Thanks for your help. Every dollar saved will be useful as I am a student.