Can your Dell Inspiron 530 take a second video card?
If this is it:
http://www.trustedreviews.com/pcs/re...nspiron-530/p2
I have to say it does not look like it has a spare PCIe slot.
If so, you will need to get an old-school PCI video card to run a third monitor, which are still available, but none of the above.
Also, if your system is the same as I just linked to, the 8600GT video card it has should be fine to run a 2560x1600 screen in the future.