Windows 7: change the name of computer shown in the router page

hi
how to change the name of comptuer that dhcp recognizes ?
i mean my computer name is SMT and in the ddwrt router page it is shown as some some other name .. the name of the shop from which i purchased the system..

how to change that ?
changing hostname has no effect .. reseting the router has no effect ..

EDIT
it turns out that i have reserved the ip in my ddwrt router for the pc and in ddwrt i have to enter the hostname ,ip , and mac at the time of reservation ..
and that was the issue .. as at the time of reservation i have used one name .. later i changed it to soething else.

now i am haivng another issue .. another another laptop running windows 7 shows itself as * in the status > active clients in my ddwwrt routers page. That page has a table which shows ip mac and the hostname .. how can i change the host name the pc shows to the ddwwrt ?

This is quite easy - SysInternals released a small program that was capable of doing this for you - The program is called "NewSID" - Basically you give it a new SID and it goes through your entire system and changes this for you.

Here is a link for this program: Microsoft Sysinternals – New SID Tool. | Microsoft | Downloads for Information Technology Professionals. Microsoft, Linux, Cisco & Apple.

If you get stuck, inbox me and let me know.

But isn't it a sort of sysprep where it removes all the system specific info? Like to whom it is registered and what is the license key and status etc?

Is the name of computer shown next to ip and mac address in the router info page called sid?
I have added a new windows 7 machine who's name is win7 but the routers list of active clients it is shown as *


Is it the only way?