In general practice, Win10 will probably not run any worse than Windows 7 does. If you are able to live with the performance limitations of running on 3GB of memory, you have nothing to loose by trying out Win10. I'd make sure the most recent BIOS is running on the machine if you try to upgrade, and as always do a good full backup before you make the attempt. If you use Dell Quickset for display control functionality, you'll need to search for at least version 8.2.20 for Windows Vista on the Dell website.
Worst comes to worse, you also ought to be able to throw any decent Linux distro on it if you want.
BTW, you can probably get a compatible 2GB DDR2 SODIMM for less than $10 on eBay to kick the memory up to 4GB. I also recall several people reporting in the Dell forums getting it to run with 6GB on that model using a 2GB and a 4GB module (even though 2x2GB is supposed to be the limit of the Intel GM965 chipset). It is only worth trying, though, if you can find a cheap 4GB DDR2 PC2-5300 or PC2-6400 SODIMM (as even used 4GB DDR2 SODIMMs usually run over $40 each).