Help with CPU and video card

ok i have a hp zd8000 laptop, with a p4 3.2ghz it also has a ati x300 vid card. And 2gb of ram.
I was given an hp desk top. I am running WOW right now on my laptop at very lowest setting at about 25-30fps.
I know from reading the post that the video card in this hp desktop is bad, But will it run wow at a little higher setting good say like 30-45 fps in 10man? I also saw a thread that said to install a ati 5450, i am a student all i have is about 100 dollars , and i read i can use the existing 250w power supply with this card.

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Processor
AMD Athlon™ II
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Processor Speed
2.8GHz
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System Bus
4000MHz
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Cache Memory
1MB on die Level 2
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System Memory (RAM)
6GB
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System Memory (RAM) Expandable To
16GB
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Type of Memory (RAM)
DDR3 SDRAM
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Hard Drive Type
SATA (7200 rpm)
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Hard Drive Size
1TB
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Graphics
ATI Radeon HD 4200
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Video Memory
256MB
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Audio
High-definition (7.1-channel surround capability)
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Speakers
None
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Network Card
Built-in 10/100Base-T
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Wireless Networking
None
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Recordable DVD Drive
Yes, double-layer DVD±RW/CD-RW
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Recordable DVD Drive Speeds
12x DVD+R DL; 12x DVD-R DL; 16x8x16 DVD+RW; 16x6x16 DVD-RW; 12x DVD-RAM; 40x32x40 CD-RW
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Direct-Disc Labeling
Yes
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Digital Media Reader or Slots
Yes, digital media card reader
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Available Expansion Bays
External: 1 (3.5" ), 1 (5.25" ); Internal: 1 (3.5" )
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Available Expansion Slots
1 PCI Express x16, 3 PCI Express x1, 1 MiniCard
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USB 2.0 Ports
6 (2 front, 4 rear)

Hey could get a card like the Radeon HD 4650 which could play the game at a higher setting. Its at around $58.99.

Some other decent choice could be:

Radeon HD 4850
Radoen HD 5670
GeForce GTS 250