This is an extremely controversial point in search engine optimization theory: the importance of linking. At some point, the major search engines realized that if a lot of websites linked to one particular site, then that site was probably important. For example, if there are a thousand websites that all have the words "search engine" linked to the Google home page, then Google's probably a highly-regarded search engine site.
This is the basis for the value search engines now place on links. Having a lot of links pointing to your site, and to pages within your site, is a very good indicator of your site's usefulness to the internet world. However, there are also many webmasters and SEO firms that use spam and other illegitimate methods to try to artificially swell their link statistics. The search engines tend to penalize this kind of behaviour very, very harshly.
Links pointing to your site are valuable depending on the value of the site that's linking to you, the value of the page on the site that holds your link, and the value of the link itself.
The value of the site depends on how relevant it is to your site's focus...for example, a link from a car sales site will not help your site much if your organization works with children with special needs. On the other hand, a link from a site that is closely related could help you a lot. The number of links pointing to that site, it's page rank, and a variety of other factors influence how highly the search engines think of it. University sites (with an .edu ending) are generally very highly regarded, as are government sites (.gov endings), so if your organization works with either educational institutions or governmental agencies, getting a link from their site(s) to yours could prove very valuable.
The page your link is one should, ideally, also be closely related to your site's focus. For example, a link on a page that lists resources for children with special needs might be great for your organization, while a link on a more random, less connected page might be worth much less, or nothing at all.
Lastly, the link itself can carry more or less value. If it's on a page with a hundred other links, it's worth nothing at all. If it's the only outbound (off-site) link on that page, on the other hand, it could be worth much more. Of paramount importance here is the link text that's actually linked to your site.
For example, if I were to add a link to my blog on the Digital Divide Network on this site, and link the words "my blog" to the URL of my blog, then I'm helping my blog's rankings for the search terms "my blog" ...and any related terms. This isn't very helpful. If, on the other hand, I link the words "Dave Chakrabarti's blog on community technology" to the same URL, I'm giving my blog a much more valuable link.
Using these ideas, you can begin to think about the links that are pointing to your site, and how to increase their number and value. One way is to use intelligent link texts and place a valuable link to your site in the signature line of your posts to online forum sites...these forums are often indexed by search engines, and a link to your site from there may have a positive influence on your rankings.
I can't say this strongly enough: Never spam.. No matter how much you might be tempted, don't spam other people's blogs or forums just to try to increase the number of links to your site. It never works...people will just find your posts and remove them, and you'll earn their undying hatred. It's not a tactic you want to use for your nonprofit, believe me. And nor is it one you need.
