Check the dell power supply rating first; if it's 320 watts or higher and you plan on using onboard video, then it may work fine with the new board. If you currently have a dell windows coa, then getting another dell board used on ebay may make sense, but most of the newer ones are priced too high. Here's a combo priced from newegg versus a used dell board:
Used dell board with backplate (pretty good price): http://www.ebay.com/itm/Dell-HY9JP-OptiPlex-790-Motherboard-Socket-1155-w-Rear-Case-I-O-Plate-/200766606595?pt=Motherboards&hash=item2ebe9f4d03.
Recommended ram with dell: http://www.newegg.com/Product/Product.aspx?Item=N82E16820147094
($46.98 for two sticks)
Non dell board: http://www.newegg.com/Product/Product.aspx?Item=N82E16813138352http://www.newegg.com/Product/Product.aspx?Item=N82E16819116504
(you can get the home version cheaper, but pro lets you use old xp files)
The dell board is for sandy bridge only and won't overclock, so a 2500 or 2600 non K cpu is recommended; they are cheaper than the K versions with unlocked multiplier. I found a 2600 used for $150 recently on craigslist. If you want a newer dell ivy bridge board, then you might as well go with the biostar and get a separate windows coa if needed. Any newer board than the one I found used will be priced too high. Sell your old dell board as a combo special on craigslist or ebay; it's worth about $125-150 used with the cpu/board/ram. This will help you pay for the new combo.