This is your main issue since you will have to figure out
a way that this DYNAMIC IP can be (securely) registered
to point to your web server, and available to the public
Internet users.

The second issue is mapping your external address (on port
80) for web access to your server behind your DSL router.

Presuming your LinkSys is also the WAN-Internet router...
(or could put a Windows machine in that position but the
level of knowledge to get the security right is then VERY
high.)

Most of the later (e.g., G) routers support both mapping external
connections (on some port) to internal machines (IP-Port);
they call this feature by various names, service definition,
service mapping, port mapping.  You get the idea since we are
defining or mapping an external port or service connection to
an actual internal IP and port combination.

So you need to do the mapping AND you need to find
a DYNAMIC DNS service.

For Dynamic DNS I use the free (they sell stuff but the
basic features you need are available free) DynDNS.com

   http://www.dyndns.com/

Basically you do this:

   1) Setup a DynDNS account and (various) dynamic name(s)

   2) Find out how your ROUTER (WAN DSL) supports dynamic
       registration (that's a LinkSys question but it probably does.)
       Configure it to update the DynDNS account above.
       Another value of DynDNS is that it is one of the most
       popular services and likely to be support semi-automatically
       by your router.

   3) Set a CNAME record for your Web server to resolve
       the NAME to the DynDNS name.

So you pick some DynDNS name like:

   YourChoiceHJohn.DynDNS.org

You set a CNAME (in your own zone, e.g., yourcompany.com)
like WWW to point to that:

   www  -->>  YourChoiceHJohn.DynDNS.org

Your router updates it's dynamic address to DynDNS every
time the address changes (reboot, lease expiration, etc.)

And when people lookup www.yourcompany.com it is mapped
to your dynamic record which has the correct address.

If you have more than one of these you just keep mapping more
CNAME records to the same or different DynDNS.com
records.