PC performance

hello every one , I would like to enquire how can I speed up my PC performance buy changing its parts or its settings and are its specs compatible with each other?...here is my PC specs:
SiSoftware Sandra

System
Host Name : HAPPINES-D71044
User : Happiness
Workgroup : WORKGROUP

Processor
Model : Intel(R) Core(TM)2 Duo CPU E8400 @ 3.00GHz
Speed : 3GHz
Cores per Processor : 2 Unit(s)
Threads per Core : 1 Unit(s)
Type : Dual-Core
Internal Data Cache : 2x 32kB, Synchronous, Write-Thru, 8-way, 64 byte line size
L2 On-board Cache : 6MB, ECC, Synchronous, ATC, 24-way, 64 byte line size, 2 threads sharing

System
System : Gigabyte Technology Co., Ltd. EP43-DS3L
Mainboard : Gigabyte Technology Co., Ltd. EP43-DS3L
Bus(es) : PCI PCIe USB
Multi-Processor (MP) Support : No
Multi-Processor Advanced PIC (APIC) : No
System BIOS : Award Software International, Inc. F8
Total Memory : 3.25GB

Chipset
Model : Giga-Byte EP43-DS3L(2E20)
Front Side Bus Speed : 4x 333MHz (1.33GHz)

Video System
Adapter : NVIDIA GeForce 8500 GT (1GB DDR2, PCIe 1.00 x16, PS 3.0, VS 3.0)

Physical Storage Devices
MAXTOR STM3250310AS 250GB (SATA300, NCQ, 8MB Cache) : 233GB (C (E (F (G (H (I (J
WDC WD2500AAJS-00B4A0 3.5" 250GB (SATA300, 7200rpm, NCQ, 8MB Cache) : 233GB (D (K (L (M:) (N:) (O:) (P:)
HL-DT-ST DVD-RAM GH22NP20 (ATAPI66, DVD+-RW, CD-RW, 2MB Cache, 192kB Flash) : N/A (Q:)
HL-DT-ST DVDRAM GSA-H42N (ATAPI66, DVD+-RW, CD-RW, 2MB Cache) : N/A (R:)
TYLW NCDQVOTMJ (SCSI, BD-R, HD-DVD-R, DVD+-R-DL, CD-R) : N/A

I guess it depends on what you mean by "speed up my PC performance." If you are talking about games, then yes a new graphics card is in order.