at least you need use url http://xxxxxxxxx:8080 to access your pc.

Do you mean though the university's LAN ?  Or is your laptop connected directly
to the Net proper (a dial-up connection to your ISP or something like that) ?
If it's the former then there should be no problem (except see below), if the
latter then you will have to take care ensuring that you are adequately
protected against attacks from the Net.

In either case it's probable that the firewall built into XP is blocking
inbound connections on the port 8080.  I believe it does by default (as it
damned well should!).  But don't just open up ports until after you have
thought the security implications.  It's no use being able to access your
webserver from your Linux box if in the process you loose control of your
laptop.

If the laptop /is/ connected directly to the Net, then you Linux box will have
to connect to it via the university's LAN, and thus it will have to connect
through whatever protection the admin people have put around the LAN.  There
are at least two potential problems: one is that they may not allow outbound
connections to port 8080 at all, another is that they may not allow connections
to servers hosted on a "domestic" ISP.  Which, if either, is actually a problem
will depend on your system admin people and how hard-line security minded they
are.  If you are connecting the laptop to their LAN rather than a dialup then
neither of these should affect you.

Once you have managed to make a connection between the Linux box and the
laptop, this /may/ cause another problem.  I'm not sure about Tomcat
specifically, but most HTTP servers are capable of multi-hosting.  That means
they use the hostname (e.g. "java.sun.com") embedded in the HTTP request to
decide which of several apparently independent websites they are pretending to
be.  If you type a numerical IP address into Firefox (or whatever) then the
hostname which is sent to the server will also be numerical, and so the server
may get confused about which of its websites it should emulate.  You should get
/some/ response, though, even if it's not the response you want ;-)

   -- chris

Routing and firewalls are the most likely reason. Without more information than
xxxxxxxx it's impossible to say.

Are both systems on the same subnet? If not, how are packets routed between
them?
Does the XP system have Windows firewall (or some other firewall) enabled which
is blocking port 8080?

I don't do philosophy.

Both computers are connected directly to the wall. So they are through
university's LAN.

I have just tried vncserver(virtual networking computing server). Start
vncsever in my notebook Windows XP. From my linux computer, I can
successfully access notebook computer in a web browser:
http://notebook.ip.address:5800
(vncserver listens http at port 5800 by default)

Now try Tomcat. Start Tomcat server in notebook computer. In the linux
box web browser, http://notebook.ip.address:8080 has nothing. In the
notebook web browser, http://localhost:8080 shows tomcat is running.

I am very confused. I am doing this is to have them for me to practice
JSP, CGI tutorials.

Thank you very much for your help.