Does anyone know what types of links are needed in order for a search engine to pick up on them ?

Search Engines rank a site based partially on "link popularity".

I recently tested my site using netscape's website garage and it came back saying that it couldn't find any links to my site. In actuality, I have many links to my site from other websites.

Does a link back to your website have to be in text format (eg. http://www.golfrevelations.com ), or is a logo okay (my company's logo displayed with the address included as a link back) etc. for search engines to pick up on it ?