Graphics card help needed before I spend money!!

According to my system I have the following for a graphics card.

Display Devices
---------------
Card name: Intel(R) 82945G Express Chipset Family
Manufacturer: Intel Corporation
Chip type: Intel(R) 82945G Express Chipset Family
DAC type: Internal
Device Key: Enum\PCI\VEN_8086&DEV_2772&SUBSYS_01D21028&REV_02
Display Memory: 256 MB
Dedicated Memory: 0 MB
Shared Memory: 256 MB
Current Mode: 1440 x 900 (32 bit) (60Hz)
Monitor Name: HP 2009 Series Wide LCD Monitor
Monitor Model: HP 2009
Monitor Id: HWP2827
Native Mode: 1600 x 900(p) (60.000Hz)
Output Type: HD15
Driver Name: igdumd32.dll
Driver File Version: 8.15.0010.1825 (English)
Driver Version: 8.15.10.1825
DDI Version: 9Ex
Driver Model: WDDM 1.0
Driver Attributes: Final Retail
Driver Date/Size: 6/16/2009 18:28:18, 3829760 bytes
WHQL Logo'd: Yes
WHQL Date Stamp:
Device Identifier: {D7B78E66-6432-11CF-B974-D821A2C2C535}

My main problem with it is I cannot get the high screen resolution I want for my new screen. I was looking at buying a 256mb graphics card which according to the shop will allow me to get a 1600x900 60hz the optium resolution for my screen. Looking at what it says here though my intergrated graphics are already 256mb.

Can someone tell me is there a difference having a dedicated graphics card to intergrated graphics card and am I buying something which will benefit my computer or am I just wasting my money.

Help gratefully received!

Thats excellent mate. I am going to put a PCIE Graphics card in. its ony 20 quid but it means I can do what I want to do with it and watch DVD's without annoying lines!

Just I did this system analysis on what my intergrated graphics was then saw 256mb and couldnt help but think I was just wasting my money on another 256mb graphic card!

So when I fit the dedicated graphics card does that mean in theory my PC should run quicker because all the memory is dedicated to the PC and not the graphics?

Cheers