Graphics Card Help for HP s3323w

Alright, I got a new PC not to long ago, and I love the GFX card thats on it, ( compared to my old intel one )but I want to get a better one.

Only problem is that the tower is incredibly tiny.
Small
Mini
Etc

Now, I have an HP s3323w






And I've got specs from DxDiag.

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- Taken from DxDiag
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System Information
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Time of this report: 3/30/2008, 21:42:18
Machine name: JOHNNY-PC
Operating System: Windows Vista™ Home Premium (6.0, Build 6000) (6000.vista_ldr.071023-1545)
Language: English (Regional Setting: English)
System Manufacturer: HP-Pavilion
System Model: GX628AA-ABA s3323w
BIOS: Phoenix - AwardBIOS v6.00PG
Processor: AMD Athlon(tm) 64 X2 Dual Core Processor 4800+ (2 CPUs), ~2.5GHz
Memory: 894MB RAM
Page File: 1634MB used, 425MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 10
DX Setup Parameters: Not found
DxDiag Version: 6.00.6000.16386 32bit Unicode
DxDiag Previously: Crashed in system information (stage 4)

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DxDiag Notes
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Display Tab 1: No problems found.
Sound Tab 1: No problems found.
Sound Tab 2: No problems found.
Input Tab: No problems found.

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DirectX Debug Levels
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Direct3D: 0/4 (retail)
DirectDraw: 0/4 (retail)
DirectInput: 0/5 (retail)
DirectMusic: 0/5 (retail)
DirectPlay: 0/9 (retail)
DirectSound: 0/5 (retail)
DirectShow: 0/6 (retail)

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Display Devices
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Card name: NVIDIA GeForce 6150SE nForce 430
Manufacturer: NVIDIA
Chip type: GeForce 6150SE nForce 430
DAC type: Integrated RAMDAC
Device Key: Enum\PCI\VEN_10DE&DEV_03D0&SUBSYS_2A66103C&REV_A2
Display Memory: 313 MB
Dedicated Memory: 122 MB
Shared Memory: 191 MB
Current Mode: 1024 x 768 (32 bit) (75Hz)
Monitor: Generic PnP Monitor
Driver Name: nvd3dum.dll
Driver Version: 7.15.0011.6222 (English)
DDI Version: 9Ex
Driver Attributes: Final Retail
Driver Date/Size: 7/6/2007 20:45:00, 4788224 bytes
WHQL Logo'd: Yes
WHQL Date Stamp:
Device Identifier: {D7B71E3E-4090-11CF-C26B-6D0A02C2CA35}
Vendor ID: 0x10DE
Device ID: 0x03D0
SubSys ID: 0x2A66103C
Revision ID: 0x00A2
Revision ID: 0x00A2
Video Accel:

Please help