how do i connect dell wireless keyboard and mouse

You need to enter a bluetooth code for your mouse and keyboard, factory default is 0000 (zeros).  You can do this by double clicking the bluetooth startup icon in the lower right corner of the taskbar or go to Control Panel and select Bluetooth then select Find Device, then you will be prompted to enter your code (0000).

the thing is i have bought a brand new xps with dell wireless keyboard and mouse and i followed the procedure as stated earlier and its still not working

Try checking the Device Manager to check if Bluetooth is enabled and the drivers are in order.  Device Manager - Start >  Right click Computer (My Computer for XP) > Properties > Device Manager > Hardware Tab if XP.  A red X means it needs to be enabled,  a red circle means it is not working properly, and a yellow ? means it needs a driver.  Another thing is to enter setup (F2 at Dell splash screen) and expand Wireless from the left hand side (bluetooth should be an option) and make sure everything is in order there.  I can't really think of anything else.