Your Dell 1720 uses an Intel Pentium T2370 processor, which was classed as a 'Merom' processor. (Source:
https://ark.intel.com/content/www/us/en/ark/products/34445/intel-pentium-processor-t2370-1m-cache-1-73-ghz-533-mhz-fsb.html )
Merom processors can't support the drivers for Windows 10, either as a 32-bit or 64-bit operating system. (Source:
https://www.intel.co.uk/content/www/uk/en/support/articles/000006105/processors.html )
So, although you might be able to load Windows 10 onto the machine, it would continue to try to use older drivers and probably run at a crawl.
I recently made the mistake of putting Windows 10 onto an old laptop, which resulted in me having a machine where the video driver simply couldn't handle streaming content (e.g. from Youtube or BBC News) without constant stuttering. I tried every trick I know to resolve the problem but I still ended up buying another laptop!