|Grasshopper is right.|
It looks like you only have a 250W power supply which isn't much. I couldn't find information on that your power supply has in terms of connectors but your $100 budget won't go too far. You'll need a power supply with a higher wattage rating then the video card you want to buy.
For example: XFX GT220XYHF2 GeForce GT 220 512MB PCI-E
"System Requirements: Minimum 350W Power Supply Requirement"
And that's a $60 card. So if I look for a decent power supply: Thermaltake TR2 W0070RUC 430W
That's a $45 power supply. Yeah there's a Linkworld LPJ2-23-P4 430W for $12.49 but you shouldn't go cheap with the power supply. Also, if the recommended power supply is 350W, don't get a 350W power supply,
AMD Phenom II X2 550 @ 3.11
Patriot PC2-6400 4Gig
Seagate 160Gig SATA
Seagate 320Gig SATA