If you still have the original box that it shipped in it would have it on this box on its label. I keep my laptop purchase boxes but most dont. I wish they put the Windows XP Home key on the box because my netbook had its paper key rub off from heavy use.
Some BIOS's have this info in them, but not all. Knowing all original specs, and an idea of what model is similar to it, you can usually pinpoint the exact model. If its a healthy computer and drivers are all installed and functional its even better because you can write down what chipset and driver is used and then know down to the main board level what you have for a main board as well since most of the hardware would be integrated to it with exception to CPU, NIC, RAM, Hard Drive or SSD, and sometimes GPU/Video Card. *If the computer isnt functional because it needs an OS added to it then your alternative to finding out what hardware you have would be to either boot off of a linux OS DVD or USB stick and see what hardware is detected or open the laptop up and read the silk screen of the main board and verify identification on chips to know what chips/chipsets are used. However with Linux it can list a generic driver being used that works with a range of chips universally so its not completely perfect.
