The quick answer to most major label computer manufacturers, including Dell, is no.
There is very little possibility of overclocking your computer, due to the motherboard's BIOS.
However, older motherboards can be found rather cheaply and the major manufacturers (like, ASUS, DFI, MSI) have used some form of overclocking on their board's BIOS. If you really want to o/c your computer, the motherboard will have to let you do so.