Here is the configuration
Inspiron 6400  Intel® Core™ 2 Duo T5600 (1.83GHz, 2MB L2 Cache, 667MHz FSB) 
LCD Panel  15.4 inch Wide Screen XGA Display with TrueLife™(glossy) 
Memory  1GB Shared Dual Channel DDR2 SDRAM at 533MHz, 2 Dimm 
Video Card  256MB ATI MOBILITY™ RADEON® X1400 HyperMemory™ 
Hard Drive  120GB 5400rpm SATA Hard Drive 
Operating System (Office software not included)  Genuine Windows Vista™ Home Basic 
Network Card and Modem  Integrated 10/100 Network Card and Modem 
Adobe Software  Adobe® Acrobat® Reader 7.0 
Optical Drive  8X CD/DVD Burner (DVD+/-RW) with double-layer DVD+R write capability 
Sound Options  Integrated Sound Blaster® Audigy™HD Software Edition 
Wireless Networking Cards  Dell Wireless 1390 802.11b/g Mini Card (54Mbps) 
Office Productivity Software (Pre-Installed)  No productivity suite- Includes Microsoft Works 8. DOES NOT INCLUDE MS WORD 
Anti-Virus/Security Suite (Pre-installed)  McAfee Security Center 30-day trial 
Primary Battery  85 WHr 9-cell Lithium Ion Primary Battery 
Warranty & Service  1 Year Mail-in Economy Plan 
DIAL-UP INTERNET ACCESS  6 Months of America Online Membership Included 
Digital Imaging  Corel Snapfire Basic – Organize and Edit your photos 
Miscellaneous  6400 dual 
Media Direct  Media Direct 3.0 
Bluetooth Options  Dell Wireless 355 Bluetooth Internal (2.0 + Enhanced Data Rate) 
Purchase Intent  Purchase is not intended for resale. 
Processor Branding  Intel Core 2 Duo Processor 
Labels  Windows Vista™ Basic 
🙂 right now i am making this post from this laptop 😀
Thanks goes to Faruk Ahmed , who helps me to got it.