Machines Causing Lag When I Walk Away

[OriginalName]

So whenever im playing voltz either on my single player world(s) or my server that me and my friends play on whenever i place machines like generators, purifaction chambers, smelters, etc. they work fine till i walk away. Once i walk like 20ish blocks away i lag EXTREMELY BAD. Major lag spikes until i return to the machines. This only happens on voltz, not tekkit, FTB, vanilla, etc. Please does anyone know how i fix this. Here are my specifications from DirectX Diagnostic:

Operating System: Windows XP Professional (5.1, Build 2600) Service Pack 3 (2600.xpsp_sp3_gdr.130307-0422)

System Model: OptiPlex 745

Processor: Intel® Pentium® 4 CPU 3.20GHz (2 CPUs)

Memory: 2046MB RAM

DirectX Version: DirectX 9.0c (4.09.0000.0904)

Video Card: NVIDIA GeForce GT 520