The Pentium M started around early 2002/2003, for about 5yrs. It hasn't been in production like Vista for about 10yrs. Frankly, it's time to upgrade. It doesn't even support a 64bit OS!
Even going to Windows 8.1 seems like an odd choice, when 10 is out and has been solid and stable. New PC's with more clock speed, more ram, more cores can be had for under $300. It'll even come with a copy of WIndows in many cases. I'm currently using a 5yr old AMD powered system with 8GB of RAM and 6 cores, and it's plenty for my general web stuff, transcoding videos, and a run a linux VM or two as needed.