c2d era laptop. first step if you haven't yet, swap the hdd for a low-cost sata ssd if you can. if you have some homeless sodimms, up the ram, too, if it won't cost anything to do it.
if you're going with mx, you want the fluxbox spin; or opt for antix with icewm instead.
otherwise start with a debian base install (no de or extra sw at install), then add only what you need. peppermint is another option--a basic debian with xfce out-of-the-box and little else. it's what i've been using lately on similar hardware.
for something 'different', you could look at slax.