Thanks for the replies. Well, when I got home and rebooted VL, and both gslapt and slapt-get at a terminal are working now! So that's one problem solved -- nothing a little reboot couldn't fix, apparently.
However, I still cannot compile other packages from source. For example, I want to install Skype. First I tried vpackager > build/install from cruxports4slack > display available > contrib, selected Skype, clicked "Build Current", chose "Target Distro: VectorLinux 6.0" and checked "resolve dependencies", then clicked "Begin". I instantly get a "FAILED" message, saying "Error 404: Not Found". So then I tried vpackager > build/install from compressed source, selected the Skype source tarball which I downloaded from the Skype web site, and clicked "Next". This results in what looks like a bunch of items being unpacked (a pile of PNGs and stuff), but then it says "vpackager is unable to recognize the nature of this source package ~ Aborting build process now" and "FAILED".