How to increase RAM for ATI Radeon HD 4200?

I have a single DVD and Hard Drive, but I have a Quad-core AMD Phenom II X4 810.
What do you guys think of the Nvidia GT 240?
Aside from that, the Radeon HD 4670/5570 look like viable options, as well as the 5670, though it would be a stretch.
I would prefer to go with the 5670, and if anyone had any ideas as to how to stretch my power supply a bit so as to get the 5670 in there, that would be awesome.
 

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At a glance

Windows 7 ProfessionalIntel i7-620M4 GB DDR3 1066 MhZGeforce GT 330M
Computer type
PC/Desktop
Computer Manufacturer/Model Number
Apple Macbook Pro
OS
Windows 7 Professional
CPU
Intel i7-620M
Motherboard
Apple Logic Board
Memory
4 GB DDR3 1066 MhZ
Graphics Card(s)
Geforce GT 330M
Monitor(s) Displays
Asus VE278Q
Screen Resolution
1440x900 and 1920x1080p
Hard Drives
1 500GB Hitachi 5400rpm HDD (Win7 Partition: 150 GB)
PSU
85 W
Case
Apple
Cooling
Apple
Antivirus
AVG Free
Browser
Chrome
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