I have a site that's been around for about 4 years and has built a good number of links and a decent ranking.
I would like to incorporate this site into a new, larger site (on a new domain) that I'm building, but I want to make sure that all the history and links that this domain has built up get passed to the appropriate section on the new domain.
Can this be done with simple mod-rewrites, or what? Is there a way to completely preserve the power of all preexisting links and SE history?
301 redirects are your best bet. Do understand that your rankings will dip for a while. It will take the SEs quite some time to sort things out. You'll want to contact linking sites and have them update their links to you.