@AC Re: Which flavor folks?
My suggestion: Buy a 32GB PATA SSD (I assume your old laptop uses a 2.5" PATA/IDE drive), you can get a Kingspec drive on e-bay from a chinese supplier for about £40. I did that for my 8-year old Acer Travelmate and installed Mint 13 LTS - works very nicely thank you. A Linux distribution with a big set of installed software will easily fit into 8GB leaving room for lots of personal data or multi-boot installations. Because it's PATA, there is a 100Mb/s limit to the possible data rate from the drive, but it's silent and robust. (If your laptop has a SATA drive, just buy a small SATA SSD.)
With an older and less powerful laptop, LXDE would be less sluggish than MATE (as I found) but there are other Linux distributiions and even lighter-weight DE possibilities out there.
With Linux, you can keep copies of any installed image on an external hard drive (use a Gparted live CD or similar to make partition copies) then you can recover from the inevitable foul-ups as you experiment. A Boot Repair Disk live CD is also a good thing to get and use. Good luck - have fun.