Distro does not matter
As far as being lightweight goes, use XFCE or LXDE

>>55175632
>lightweight
>a DE

>>55175673
>caring about 100-200mb of ram
Even with only 512mb of ram, which most p4 machines would have stock, it's not a big deal.

Less than 512mb? Like 256? Go Windowmaker/GNUStep
128mb, either fucking upgrade or use a basic wm like i3/subtle

arch + openbox/i3

>>55175748
>20-40% is not a big deal
May your hands be cursed with temporary arthritis so that you type and move your mouse 20-40% slower.

Seriously though it's just the comedy of picking between DEs at all when going "lightweight." You don't compare Big Macs to Whoppers when on a diet, you go home and eat a salad.

>>55175612
any distro is good on any computer it all depends on all the shit you install.

if you wanna go lightweight install arch, debian sid, gentoo, or slackware. these are good distros i have used and can recommend.
then once youre done install openbox, i3 or ratpoison. they are all flexible and lightweight but you should read into how they behave before you decide, as they are all pretty different.

Alpine Linux

>>55176603
Yeah I'm delving into this kinda blind. Been stuck on windows machines my whole life, but I used to mess around with DOS awhile back.

Thanks everyone that's given advice so far. I tried a more windows looking interface a little while back on this computer but it lagged like crazy and I got discouraged and had less free time to learn anything.

Go to distrowatch and search for distros for old computers
http://distrowatch.com/search.php?ostype=All&category=Old+Computers&origin=All&basedon=All&notbasedon=None&desktop=All&architecture=All&package=All&rolling=All&isosize=All&netinstall=All&status=Active

>>55176792
that said my choice would be Antix or Puppy

>>55176711
Try something with XFce if you want lightweight and windows-like.