minecraft lag機原因和解決方法

我玩minecraft SP 1.2 會會疾下疾下
而我的電腦配備是..

Processor: Intel(R) Celeron(R) CPU 430 @ 1.80GHz
Memory: 1014MB RAM
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Display Devices
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Card name: Intel(R) G33/G31 Express Chipset Family
Manufacturer: Intel Corporation
Chip type: Intel(R) GMA 3100
DAC type: Internal
Device Key: Enum\PCI\VEN_8086&DEV_29C2&SUBSYS_82B01043&REV_10
Display Memory: 256.0 MB
Current Mode: 1024 x 768 (32 bit) (60Hz)
Monitor: Monitor Max Res: 1600,1200
Driver Name: igxprd32.dll
Driver Version: 6.14.0010.4926 (English)
DDI Version: 9 (or higher)
Driver Attributes: Final Retail
Driver Date/Size: 2/15/2008 13:12:06, 57344 bytes
minecraft中我已把全部特效關掉，視野最近
請指出lag的原因
盡可能教我如何改善(唔要買果部機，買新零件)
謝謝