Pentium M with Windows XP should be ok if you're not expecting too much of it, but you do need more than 512 MB of RAM for today's software.
Your laptop probably has two memory slots. If only one is occupied and it uses DDR2 then you're in luck - you can simply add another SODIMM (memory module). I have a Hynix 512MB PC2-4200 (OEM from HP) module right here that I took out of my Pentium M laptop. I don't need it.