Hidden Text for search purposes

Can I insert hidden text to a product and have search pick it up? For example: a "Model Number" from the competition that i don't want them to see on my site but that will show up if you search for it?

This is consider spamming by Search Engines and you may get punished for that.

If you don't want it to show as part of the viewable product page content, you could add it as part of the product's custom keywords ... that way it'll only show up in the metatags, and will also be included as part of the search results. That should also get around the spam issue.

this is intended for search inside my site. it's the products that need to have the hidden text and not the pages. my search engine (google) standing is another matter completely.

Stuffing the extra words into your custom metatags is the fastest and simplest solution.
If you want another solution, post in the Commercial Help Wanted area for paid assistance from someone who has the skill to add new database fields, change search criteria, and build admin interfaces for collecting, managing, editing, and storing the additional information you desire.