Your best bet is a cpu upgrade. Starmicro has the SL8VQ core duo t2400 for $48 for the bare cpu only. The t2700 is also available for $170, but that's a poor price/performance deal. The motherboard you have can't be changed out easily; a standard micro atx board may be too large for your case. A mini-itx board will be limited in the choice of cpus; most are slower than your current cpu.