The best thing to do would be to find someone who is fluent in both vbs and shell scripting in order to have them convert the script for you. This may cost some money, especially depending on the size of the project.

The thing of it is, is that most windows scripting languages are very task oriented - there are certain aspects of the operating system that a particular scripting language is meant to be used for administrating. Shell scripting on the other hand is simply a collection of tools that are available on almost all *nix distributions, bound together by an interpreter (whether it be ksh, csh, sh, or awk). There really aren't a lot of limitations there. The windows script host is an interface to the graphical options that are available in windows - whereas the graphical interface for *nix distributions are an interface to the shell commands.

I can certainly help you with this task, as I am a confident programmer with both languages (in fact, shell scripting and vbscript are my two specialties). Depending on your own ability, you may be able to do it yourself as well. Elaborate on how involved this script will be - the number of lines of code, the aim of the script, etc. and someone can give you an idea of what it is going to take - but you certainly will not find an automatic translator.