The only concern is the size of the power supply. The HD4830 needs a bigger power supply than usually ships with prebuilt systems. Other than that it will fit. Here is another card that will work on that system if the PSU is 300 to 350 watts like most HP/Dell prebuilds. http://www.newegg.com/Product/Product.aspx?Item=N82E168... The HD4670 is not far of in performance from the HD4830.
Thanks Rolli59 -- when I read the comments in Newegg...
"p.s. i had to buy separate Power Supply Unit...since the one that comes with this Lenovo is only 280watt...but newegg had a good 530 watt for 39.99 and install was a breez!!!...
i found this a cheaper root instead of buying all separate pieces for a gaming pc."
How can I know for sure what the power supply output is before I buy anything?
Yeah, the PSU in that thing is terrible. The HD4670 is the best you can get away with without a new PSU.
I highly recommend you build the system yourself however. You can build a much better system for the same money. The actual putting together of the computer is really pretty simple. It's picking out the parts that can be tricky but that's why there are message boards like this.
I support jyjjy´s suggestion of building yourself. There are plenty of folks here to help out selecting parts and the end result is that you will be happier with your rig and have more upgrade-ability than with prebuilt.
That's a little under $500 after rebates because I erred on the side of quality rather than going cheap(a few days ago with all the black friday/cyber monday deals would've been a better time to do this.) The only thing left out is a video card and that depends on what you want to spend/your resolution now that the PSU isn't a problem.