Dell inspiron 1720 supports Windows 2000 professional surely. The only thing is you should get the required motherboard utility drivers for the windows 2000 operating system.
If you are having a Dell Inspiron1720 in Windows platform. Go to BIOS and Onboard devices->Flash Cache module->Change it to Off and the go to SATA operation and Change it to ATA. Save changes and exit out of the bios and check if its working
I think its not possible. Since its difficult to find the driver files of your laptop, for windows 2000. Also you will need a third party disk formatting tool to erase your current operating system. If these tasks can be done then you can replace your current operating system with windows 2000
I have heard before that some graphic card were using DirectX 10. And on the website of DELL, the resource CD they sent to me contains the drivers for Windows Vista AND for Windows XP! As I have a long past with DELL computers.