If you want to mine, here is a simple way:
Get GUIMiner-scrypt
https://bitcointalk.org/index.php?topic=150331.0Very easy to use and it has presets for a lot of cards. Get the required downloads off that link.
Get multibit wallet.
https://multibit.org/ and create a bitcoin wallet address
Mine on middlecoin pool
http://www.middlecoin.com/ It's real easy to mine on with guiminer-scrypt. Just paste your bitcoin address and any password you make up into guiminer-scrypt and if you have a card that matches one of their presets, use the preset and off you go. Then just learn how to tweak settings and you will get a better hashrate.
This is essentially what I'm doing and I've managed to get my hashrate within 1khash of the top listed hash for my card here:
https://litecoin.info/Mining_hardware_comparisonMy recommendation is to not even bother with the nvidia card for mining. You could use that one for your display graphics and get a better gpu for mining. Best card for mining seems to be AMD HD7950 as it offers a high amount of hashes on a low power consumption.
If you decide to get a better gpu, you will need a new power supply because it seems that computer has only a 280 watt psu. Most cards recommend you having a 500w psu but you might even need a 750w. Your dell specs show the pcie slot to be 1 PCIe x16 full height graphics, -(H: 4.2" X L: 9") so make sure any card you buy fits within that. I would leave the cover off the case to not trap heat.