Yeah, that's the common sense. However there have been at least 2 fellas I've tried to help get set up but no joy. Dell has even said, "won't work"... Apparently the mobo/chipset is prohibiting the use of more than one video card.
And yes, it does have onboard video... which if you've read my stuff before, I've cautioned against getting such a computer if one intends to run multi-card rigs. (On some mobos with onboard video you can disable the onboard and run 2 video cards... but apparently not on the Vostro.)
Unless a few ET'ers chime in and say they are running quads or dualheads on Vostro, I suggest you look to the Dell Precision T3400. It has a much better mobo anyway.
If you want cheap, check out the Dell Business Outlet... just a few minutes ago I saw a T3400, 2GB of RAM, but only E4400 CPU, + NVS 290 dualhead (but that's plenty powerful enough for trading)... for $589