u can also try this, worked for me. several other methods listed in dell notebook faqs.
Run the registry editor, if you don't know how (For Windows XP):
(i) Click Start
(ii) Select run
(iii) In the presented field, type "regedit" without the quotation marks and click OK
(iv) Look under the following field using the + extensions on the left:
(v) Hopefully you will see one of the following codes:
=> One with HTC will be the Hitachi brand (such as the HTC1C46 WSXGA Display)
=> One with SHP will be the Sharp brand
=> One with SEC will be the Samsung brand (such as the SEC3150 WSXGA Display)
=> I am not sure exactly what Toshiba will be (TSH?) So I will need some feedback here, including any other brands you all find.
Sometimes your manufacturer will not be displayed in the registry, and you will be faced with 4 or 5 "Default Monitor's"... we are not sure why this happens exactly, but if you find this is the case move onto another one of the methods.