>how can i have the serial number of a computer ?

Many people use MAC address for this. However, it can be faked by custom ethernet BIOS and flashing the ROM. Still, MAC address is good choice if TRUE security is not required, but just a "cheap" session unique identifier.

Modern CPUs have a unique ID, but can be disabled by user BIOS settings, also SMP can be an issue with SMT and a lack of affinity.

There are algoriths which can retrieve the Windows Activation Key, but Windows can be illegally copied.

I guess the answer is "no, there is no easy, reliable way."

>can this function be run by sqlserver ?

On the server? Yes. Needs to call a custom DLL to obtain that information. Would be more desirable to run client-side though.

You could throw up a textbox with the prompt: "Please input serial number". :-)