The Vista drivers will work on Windows 7.  Windows 7 is basically "Vista improved" and uses the same drivers. Actually, Windows 7, when it installs, also installs drivers for a lot of devices.  You shouldn't need much from the Dell downloads.
My Inspiron 1720 is now 3,5 years old. Service is expired.I just installed Windows 7 N 32 bits on my portable. Problem is: the drivers on the drivers download site of dell (via my servicetag) are Vista drivers because my pc was deliverd with Vista 32bit. Why can't I find the right drivers for windows 7 without trouble? Where can I find the drivers for my pc and Windows 7?  
drivers for windows 7 32 bit