there are some external graphics cards that can be used via USB, but noone of them will be best than your integrated graphics card, so there is no way to Upgrade your graphics power, there is no way to upgrade notebooks graphics card.
The Dell Inspiron N5010 comes in 2 setups. I assume since you claim Intel Graphics that you're integrated graphics processing is done by the CPU on shared memory over the HM57 chipset. This is not a bad setup. You can purchase a PCMCIA card but since it's attached to the USB Host Controller...you're looking at 480mps TOPS! Definitely NOT an improvement. I suggest you FILL the memory bay to capacity (in this case 2x 4Gb PC3 1333Mhz (you can go with 1066 but 1333 is almost the exact same price...why lower the ceiling?) This way your system can "reserve" up to a gigabyte of shared memory and dedicate it to just graphics. Hope that helps