Help in selecting cheap/good hardware

Hi ,
I am completely newbie to Asterisk.
I am paying too much for my mobile every month, recently I found this article

I thought of setting up that to reduce my mobile bill. At home I am using Sunrocket VOIP phone service. I have free calls between my mobile and home phone.

Can I setup Asterisk with my VOIP service?

I have following hardware in my desktop

  1. GIGABYTE GA-K8N Pro-SLI Socket 939 NVIDIA nForce4 SLI ATX AMD Motherboard with 1394b
  2. AMD Athlon 64 3700+ San Diego 2.2GHz Socket 939 Processor Model ADA3700BNBOX

And running WinXP Home/Ubuntu Edgy on my desktop.

Could you please suggest a cheap/good hardware to setup Asterisk with my desktop?
I googled so much to find out hardware but I am confused which one to take.

Thanks in advance.