If it was my only computer, and I was starting out on Linux, i wouldn't install Slack straight away. What i would do, is do a clean format of your harddrive using http://gparted.sourceforge.net/livecd.php
to remove all trace of Vista (presuming you don't want it at all as this will remove the rescue partition etc etc). At the same time I would Partition the harddrive into 2 equal portions (presuming it is about 60gb and you can have just about enough space), then I would install quite a user friendly Distro such as Ubuntu on one partition and then when you have this up and running install Slack on the other partition.
This ensures that you can still access the internet, as you are pretty much stuffed without it when trying to get your first linux distro working. I suggest Ubuntu as (for me at least), it's pretty much out of the Box and is pretty stable. Not as hardcore as other Distros but it's a good way to cut your teeth from Win. Then if you decide that you prefer Slack or Ubuntu at a later date, simply format the other partition to free up space. The best of both worlds!!