Download CPUZ and check under Motherboard for your motherboard model,etc.
If you have a Dell/HP,etc you won't be able to OC through BIOS. However, in some cases you MAY be able to do a BSEL/volt mod to increase FSB.
I guess it really depends on what you mean by "premade" If you bought your PC off the shelf at your local Wal-Mart, your BIOS options have deliberately been disabled by the manufacturer. This undoubtedly lowers their warranty claim rate as overclocking is a good way to damage a computer. If you bought it from a local computer shop that custom built it for you, you would most likely have all BIOS options available to you.
Based on your description, you have an "off the shelf" PC and you will have no OC'n options.
Is it a brand name?? If yes It's too late to talk about overclocking
damn yea its brand name off the shelf LOL oh well im proabably going to end up building my own computer i have a qustion, do you need a PCI-slot card when makeing your own computer and do you need power protectors?
and whats this BSEL/volt overclocking you were talkin about??