Issues with an Nvidia Geforce GTX 260

Hi, I just bought a BFG GTX 260 Maxcore OC and after the install my computer is running slower than when the previous graphics card was installed which was an Ati radeon 2600 xt her this is weird because this graphics card is a mid to high end graphics card, here are my system specs:

OS Name Microsoft Windows 7 Ultimate
Version 6.1.7600 Build 7600
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Name JOSH-PC
System Manufacturer MICRO-STAR INTERNATIONAL CO.,LTD
System Model MS-7345
System Type x64-based PC
Processor Intel(R) Core(TM)2 Quad CPU Q9450 @ 2.66GHz, 2670 Mhz, 4 Core(s), 4 Logical Processor(s)
BIOS Version/Date American Megatrends Inc. V1.10, 11/10/2008
SMBIOS Version 2.5
Windows Directory C:\Windows
System Directory C:\Windows\system32
Boot Device \Device\HarddiskVolume1
Locale United States
Hardware Abstraction Layer Version = "6.1.7600.16385"
Installed Physical Memory (RAM) 4.00 GB
Total Physical Memory 4.00 GB
1 Gb Dimm- slot 1 OCZ SLI PC2-6400 OCZ2N800SRC44GK
1 Gb Dimm- slot 2 OCZ SLI PC2-6400 OCZ2N800SRC44GK
1 Gb Dimm- slot 3 CORSAIR XMS2 DHX 1GB PC2-6400
1 Gb Dimm- slot 4 CORSAIR XMS2 DHX 1GB PC2-6400
Available Physical Memory 2.36 GB
Total Virtual Memory 8.00 GB
Available Virtual Memory 6.12 GB
Page File Space 4.00 GB
Page File C:\pagefile.sys
Hard drive 1: 162.00 GB
Hard drive 2: 750.00 GB
600W PSU OCZ OCZ600SXS-B ATX

I have never owned an Nvidia product, if this is a problem where the card works better in games than real world applications, then I am sadly disappointed, if that is the case I will sell this and get an hd 4870. can you please help help?