The official Google Webmaster Central blog has a post called "A spider's view of Web 2.0" which gives pointers on creating Ajax-enhanced websites that are also understood by search engines. Here it goes:
How will Google see my site?
Design for accessibility
Develop with progressive enhancement
If you're starting from scratch, one good approach is to build your site's structure and navigation using only HTML. Then, once you have the site's pages, links, and content in place, you can spice up the appearance and interface with Ajax. Googlebot will be happy looking at the HTML, while users with modern browsers can enjoy your Ajax bonuses.
<a href="ajax.htm?foo=32" onClick="navigate('ajax.html#foo=32'); return false">foo 32</a>
Note that the static link's URL has a parameter (?foo=32) instead of a fragment (#foo=32), which is used by the Ajax code. This is important, as search engines understand URL parameters but often ignore fragments. Web developer Jeremy Keith labeled this technique as Hijax. Since you now offer static links, users and search engines can link to the exact content they want to share or reference.
While we're constantly improving our crawling capability, using HTML links remains a strong way to help us (as well as other search engines, mobile devices and users) better understand your site's structure.
Follow the guidelines
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For more, refer to Server location, cross-linking, and Web 2.0 technology.