Upgrade video card and power supply or upgrade my pc?

Question

I have a :
HP
Series Pavilion Model M8530F(KT334AA) Type Media Center / HTPC Processor AMD Phenom X4 9550(2.2GHz) Processor Main Features 64 bit Quad-Core Processor Cache Per Processor 4 x 512KB L2 Cache Memory 5GB DDR2 800 Hard Drive 750GB 7200RPM SATA Optical Drive 1 SuperMulti DVD Burner with LightScribe Technology Graphics NVIDIA GeForce 9300GE with Hybrid SLI Technology with 256MB dedicated video memory, DVI and HDMI capabilities, and support for Microsoft DirectX 10. Up to 1919MB Total Available Graphics Memory as allocated by Windows Vista Audio High Definition audio Ethernet Integrated 10/100/1000Mbps network interface Keyboard HP multimedia keyboard Mouse HP optical mouse Operating System Windows Vista Home Premium 64-bit Software Included Photo and Video
muvee autoProducer Basic: Automatically create professional looking home videos and burn to DVD
Entertainment
Cyberlink DVD Suite Deluxe: Automatically fix and edit videos and create CDs and DVDs. Edit, burn and archive data to discs.
Productivity
Microsoft Works 9: Includes a word processor, spreadsheet, database and calendar
Microsoft Office Home and Student Edition 2007 Trial: 60-day trial version
Adobe Reader 8: Read and print PDF file
PC Security
Norton Internet Security 2008: Protect your PC out of the box (60 days of complimentary live updates)
Online Services
Easy sign-up to major dial-up and broadband Internet Service Providers:
- MSN dial-up (offer included)
- NetZero Dial-Up (offer included)
- NetZero Accelerated Dial-Up (offer included)
- Juno Turbo Dial-Up (offer included)
- High Speed Internet Services Comparison Shopping
Motherboard Chipset NVIDIA GeForce 8200 Chipset
CPU CPU Type Phenom X4 Installed Qty 1 CPU Speed 9550(2.2GHz) L2 Cache Per CPU 4 x 512KB CPU Socket Type AM2+ CPU Main Features 64 bit Quad-Core Processor
Graphics GPU/VPU Type NVIDIA GeForce 9300 GE Graphics Interface PCI Express x16
Memory Memory Capacity 5GB DDR2 Memory Speed DDR2 800 Form Factor DIMM 240-pin Memory Spec 2GB x 1 & 1GB x 3 Memory Slots (Available/Total) 0/4 Maximum Memory Supported 8GB
Hard Drive HDD Capacity 750GB HDD Interface SATA HDD RPM 7200rpm
Optical Drive Optical Drive Type DVD Super Multi Optical Drive Spec SuperMulti DVD Burner with LightScribe Technology
16x DVD±R, 8x DVD+RW, 6x DVD-RW, 8x DVD+R DL, 4x DVD-R DL, 5x DVD-RAM, 16x DVD-ROM, 40x CDR, 32x CDRW, 40x CD-ROM
Audio Audio Chipset Integrated
Communications Modem 56K LAN Chipset Integrated LAN Speed 10/100/1000Mbps
Front Panel Ports Front USB 2 Front IEEE 1394 1 Front Audio Ports 2 Card Reader Front panel 15-in-1 memory card reader: supports SmartMedia, xD, MultiMedia Card, Secure Digital (SD), Mini Secure Digital, Compact Flash I, Compact Flash II, IBM Microdrive, Memory Stick, Memory Stick Pro, Memory Stick Duo, Memory Stick Pro Duo, RSMMC, MMC Mobile, MMC+
Back Panel Ports PS/2 2 Video Ports 1 DVI, 1 HDMI Rear USB 4 Rear IEEE 1394 1 RJ45 1 port Rear Audio Ports 6 ports S/P DIF 1 port
Expansion PCI Slots (Available/Total) (2/3) PCI-E x1 slots
(0/1) PCI-E x16 slot
Mouse Mouse Type HP optical mouse
Keyboard Keyboard Type HP multimedia keyboard
Physical Spec Dimensions 16.54" x 15.16" x 7.60" Weight 32.00 lbs.
Manufacturer Warranty Parts 1 year limited Labor 1 year limited
Sorry for the long copy and paste. I read that I can upgrade the video card and power supply. But atm when I play world of warcraft at ultra settings, I tend to lag really bad in the new instances with the new cat expansion that came out. I wanted to know if I should upgrade the video card and power supply for better performance or just upgrade my whole pc tower.  Fyi, I am running a Acer X243w lcd flat panel monitor if that helps too.

Answer 1

My brother has a high end laptop with a built in, high end gaming video card (I forget which one). He's able to run the game on full-on Ultra. 
I have an integrated video card which games the game on.. 'cartoon'.. mode. It's lower then low. When someone shoots a powerful spell at me, I go into a DOS Prompt. (not really, but it's pretty bad).
Funny thing is, I can still kick my brother's butt in any PVP match he wants to set up. 
But I guess his graphics are pretty....
As for which video card works best, I'd have to do some research. After that graphics update they did with CAT,  it's kind of a toss up again.
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