I have a several home computers all connected to the net through a linksys router. I'm forwarding port 80 to my Linux box, which is running apache. Right now I'm hosting my own site with a free sub-domain from dynDns. Is it possible to host other sites (also using dynDns sub-domains) on my computer? If so, what is this called... very new to apache and web stuff in general, and find myself getting confused quickly reading about virtual hosts, etc., and wondering if it can even be applied with my setup.

So basically I'd like to be able to send port 80 requests for different sites (site1.dyndns.com & site2.dyndns.com) to the one wan ip i have (router), forward those requests to my computer running apache, and have them resolve and serve their respective web-sites.

Any help, pointers, and suggestions for further reading greatly appreciated.

You can certainly do it - just point each domain to the same IP address then set up virtual hosts for each domain - see:
http://httpd.apache.org/docs-2.0/vhosts/

Thank you... that looks like it exactly.