distro optimization question

[Andrew Gould]

Background:  I'd like to learn Drupal 7.  I'm playing with it on my
Macbook via Bitnami's Drupal stack. Once I get past the very basics,
I'd like to start fresh (leaving mistakes behind) on an old (circa
2001) computer:  900MHz AMD (Athlon?), 1.5GB RAM.

Question:  When choosing a Linux distribution for older hardware, how
much do I have to worry about the base operating system as opposed to
the desktop environment?  (For example, would OpenSuse be a good
choice as long as I used LXDE instead of KDE, or should I avoid
"heavy" distributions like OpenSuse altogether?)

note:  I'm not as bright as I used to be, so I'd rather not have to
learn Slackware **and** Drupal at the same time.  ;-)

Thanks,

Andrew