If thats what you need I strongly recomend you go for Slackware instead of zipslack. The difference isnt that much except that zipslack is missing alot of stuff that you would probably want.. Also you will probably get more out of the machine with a fullblown slackware..
How old is the machine? How much diskspace, ram etc?
The default slackware boot is pretty slow IMO, but you can speed it up alot by disabling/uninstalling daemons you dont need and rescheduling the non-essential ones that you still need to boot up after initial boot. this will tell you more on that: http://www.linuxquestions.org/questi...=at+5+min+boot