It depens of want you'll do on your laptop. The XGA+ will be greater for photo editing, while the XGA will be better for reading. The characters will be bigger on a lower resolution ( 1280x800 ) than on a higher ( 1920x1200 ). For viewing movies, all options are good.
FOr the Wi-Fi, again it depends of your needs. If you play a lot of online games and share big files, then, the N will be for you. If you surf opn the Internet and send e-mail, get the Intel PRO/WIreless G solution.
i wanted to know which type of screen would be good for movie viewing. dell has the following options in Inspiron 6400
15.4" Wide Screen XGA Display
15.4" Wide Screen XGA Display with TrueLife
15.4" Wide Screen XGA+ Display with TrueLife
and in Inspiron 9400 they offer:
17" Wide Screen WXGA+ (1440X900)
17" Wide Screen UltraSharpTM WUXGA (1920x1200) with TrueLifeTM.
also which wi-fi standard i should opt for: 802.11g or 802.11n.