trusted and untrusted scanner

I am considering creating a new program for my company that would act as a preventative measure. It would probably work in a way that is not so different to ad-aware or an Anti-Virus but that will not be it's function.

The idea is to create a simple program that will carry two lists "Trusted and Approved" and "Untrusted" these would be in the form of a definition list of some kind. The program would then give a report showing that company PC n (being the PC running the scan) has installed [list]
programs that we officially approve of and [list]
programs that we have chosen "not to trust".

This "not trusted" list would include some scum-ware and rip-off spy-ware checkers that users have been installing. It would also include a number of amusing screen savers that never-the-less create copyright issues that could cost us lots of cash.

It would be nice to scan for indicators that might point to "issues" that could cause us trouble such as back doors and suspect installs that are not listed. It would be good if we could design an engine for this and supply it with "Causes for concern".

My hope is to set up a "blame free" clean-up round of the nextwork and that this would be the tool to help me do it quickly.

I would be creating this in VB6 and would love to hear how I might simply detect specific installs.

Any algorithms or code snippets welcome (as always) and I would be interested to hear if any one has tried this before.

If a large chunk of the work for this project comes from out side the company I would be willing to release the final item here on the forums under the GNU LGPL so every one can use it freely.

Ideally I'd like to use fairly open standards so that my work can be reused and others can create thier own (un)trust lists.