I just upgraded my Inspiron 1420 to Windows 8 and it works fine. First I upgraded to 4GB RAM and upgraded the BIOS to version A10, then I installed Windows 8 Pro. I added StartIsBack to restore the start button and boot to the desktop.
The only problems I had were with drivers for the touchpad and the SD card reader, both of which I solved.
3. Set the downloaded file to run in compatibility mode for Windows Vista by right-clicking the file, and choosing Properties > Compatibility, checking the box labeled "Run this program in compatibility mode for", and selecting "Windows Vista".
4. Open the downloaded file and follow the on-screen prompts to install the driver, restart your computer as requested and you should be good to go!