Low fps on most of my first shooters. Outdated computer or fixable?

[Kermit]

**Ok just to let everyone know, im a Steam/Valve fiend, meaning I play everything valve has to offer [HL, HL2, CS, CSS, CZ, NS, TF2 etc etc]**


1) Every fps I play always have dropping fps making my screen jitter. I cant even play Counter Strike 1.6 without dropping fps! This hasnt happened before. My fps started dropping after my 19' screen broke, and purchased a 22 inch that can support only 60hz. Is this my problem?

2) I dont know if i need to purchase a gaming computer or should i just buy new parts. Here is my specs. (Taken from EVEREST )

BTW if i do need a gaming pc, kindly show me what/where to buy.
If i dont need a gaming pc, but need better parts, please advise

SUMMARY===>

Computer:
Operating System Microsoft Windows XP Home Edition
OS Service Pack Service Pack 2
DirectX 4.09.00.0904 (DirectX 9.0c)
Computer Name FAMILYCOMPUTER
User Name HP_Owner

Motherboard:
CPU Type Intel Pentium 4 550, 3400 MHz (17 x 200)
Motherboard Name Asus PTGD1-LA (3 PCI, 1 PCI-E x16, 4 DDR DIMM, Audio, LAN, IEEE-1394)
Motherboard Chipset Intel Grantsdale i915P
System Memory 512 MB
BIOS Type AMI (07/26/04)
Communication Port ECP Printer Port (LPT1)

Display:
Video Adapter ATI Radeon X300/X550/X1050 Series Secondary (128 MB)
Video Adapter ATI Radeon X300/X550/X1050 Series (128 MB)
3D Accelerator ATI Radeon X300 (RV370)
Monitor Plug and Play Monitor [NoDB] (CND72432M1)

Multimedia:
Audio Adapter Intel 82801FB ICH6 - High Definition Audio Controller [B-1]

Storage:
IDE Controller Intel(R) 82801FB Ultra ATA Storage Controllers - 2651
IDE Controller Intel(R) 82801FB/FBM Ultra ATA Storage Controllers - 266F
Disk Drive WDC WD2500JD-22HBB0 (232 GB, IDE)
Disk Drive Generic USB SD Reader USB Device
Disk Drive Generic USB CF Reader USB Device
Disk Drive Generic USB SM Reader USB Device
Disk Drive Generic USB MS Reader USB Device
Disk Drive Apple iPod USB Device (27 GB, USB)
Optical Drive HL-DT-ST DVD-ROM GDR8162B (16x/48x DVD-ROM)
Optical Drive LITE-ON DVD+RW SOHW-822S
SMART Hard Disks Status OK

Partitions:
C: (NTFS) 232521 MB (164668 MB free)
D: (FAT32) 5931 MB (775 MB free)
Total Size 232.9 GB (161.6 GB free)

Input:
Keyboard HP PS2 Keyboard (2K - 3)
Mouse HID-compliant mouse

Network:
Network Adapter ARRIS TOUCHSTONE DEVICE (74.72.212.4)
Network Adapter Realtek RTL8139/810x Family Fast Ethernet NIC
Modem Agere Systems PCI Soft Modem

Peripherals:
Printer Fax
Printer hp deskjet 656c series
Printer hp photosmart 7700 series
Printer Microsoft Office Document Image Writer
Printer Microsoft XPS Document Writer
USB1 Controller Intel 82801FB ICH6 - USB Universal Host Controller [B-1]
USB1 Controller Intel 82801FB ICH6 - USB Universal Host Controller [B-1]
USB1 Controller Intel 82801FB ICH6 - USB Universal Host Controller [B-1]
USB1 Controller Intel 82801FB ICH6 - USB Universal Host Controller [B-1]
USB2 Controller Intel 82801FB ICH6 - Enhanced USB2 Controller [B-1]
USB Device ARRIS TOUCHSTONE DEVICE
USB Device USB Composite Device
USB Device USB Human Interface Device
USB Device USB Human Interface Device
USB Device USB Mass Storage Device
USB Device USB Mass Storage Device


For full report, check here