I have created a List template and have exported it
out. I want to upload this in another serve. As I
understand I can do it from Manage List Template
Gallery .When I upload this stp file, I can only see
it in the current site  and its sub sites.

My question is, how can I upload the .stp file so that
it is available in all the sites and subsites

You need to use:
stsadm.exe -o addtemplate
-filename <template filename>
-title <template title>
[-description <template description>]

This add the template in site  template listing .i have
List template which need to be uploaded.

anything other which can be done

You can create a custom list definition by copying an existing one,
rename it, modify it to fit your needs, add it to the apprpriate place
in the 60 hive, and modify the appropriate sts... onet.xml.

You would be better off createing a custom site  definition that includes
your custom list definition .

The Home page by default displays the Topic area's sub areas. If you
delete the Topic area, the Home page left  nav will display the same
areas that run across the top  nav.

If you have renamed or used the Topic area  and created sub areas
underneath it, you can create a new area and move those sub areas under
it via the Manage Portal Site admin screen, and then delete the Topic
area.

No problem... now I think I have answered it twice :-P Glad that solved
your issue.

It's good to get two answers and both be
correct when, often, we get dozens of answers and only one or less
are correct.