Google says if you have a Geforce 210 card in there, it's a PCI-e 2.0 x16 slot which will take up to the ATI 6xxx (good luck finding one) or Geforce 5xx (a 560 is pretty good). Good luck fitting a bigger card in a slimline case, and yeah you would need a better PSU. The real crux of that computer though is the E5300 processor. Not much you can do with a 775 socket unless you can find an old Q6600 or something on Ebay, and that is assuming the firmware isn't locked to only accept crappier CPUs (it probably is, but you'd have to find the documentation for your mobo).
OK I take it back, there isn't much you can do with your old setup. However, a new desktop will almost always be a better deal than a new laptop, especially if you build it yourself.
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Anyway, some other OEM manufacturers to look at: ASUS, Clevo, Compal... there's more I can't remember, but if you buy Dell, Toshiba, Lenovo, Sony, Apple, etc you are just buying through a middle-man. Some of the OEM's you can order from will even offer the same upgrade options/services as the re-brander.
Another good money-saver for laptops is to buy refurbished. Most returns for expensive electronic gizmos (laptops, tablets, etc) aren't even for actual defects. Refurbished computers are a safer buy than most people think.
Lastly, wait for stupidly outrageous sales, IE Cyber-monday etc. Lots of websites to track sales, coupons, etc for laptops specifically IE dealnews.
Also: Whoops, not the 77xx, I mean the 67xx. I'm not sure if any of the fusion setups use the 7xxx series yet. Though I have no doubt you could find a nice IvyBridge+Nvidia for cheaper than an AMD fusion setup with a sale.