it probably can, but i think you are supposed to have at least 16MB, and optimally 32MB. i have a feeling 4MB will take a bit of tweaking to run X.
you might be interested in this link:
http://gd.tuwien.ac.at/opsys/linux/baslinux/BasicLinux is a linux which is based on slackware. it is optimised for old computers with limited hardware resources. They provide really pared down slackware packages that work, but do not provide anything like the functionality of a full slack linux. also, their use of busybox, excellent though it is makes it very hit and miss installing extra software on your system, since it is always possible you could wipe out your main system utilities (like cd, rm et cetera). If i were you i would install a minimal text only slackware 9.0 and then go and thoroughly read up about basiclinux until you are confident you can follow their instructions to get X working (i am not 100% sure of what these instructions are at the moment i haven't used basiclinux since version 1.7 which was very different to its current version).
edit:
here are the instructions for adding X. I suggest as i said that you install a small slack installation with only the components you require and nothing else, then follow the X installation instructions i linked to here and see how you go. those instructions worked for me, but i was using basiclinux 1.7 (based on slack 3.5 but not as versatile) and i had 32MB.
further edit: if you are using the installation instructions for how to install X on basiclinux, but you are using slackware, use "installpkg" instead of "pkg". i would recommend using "installpkg -warn" before you actually install them too, just in case, see
man installpkg for more details.
[ May 09, 2003: Message edited by: Calum: hopelessly outnumbered ]