how to install open office,adobe reader,adobe directx and vlc player on xubuntu 7.10

OpenOffice is part of a standard install
Adobe Reader = http://www.jonathanmoeller.com/screed/?p=1622
DirectX is wrapped around with by wine which is in the repos. You can install it using software centre (remember to check appdb for compatibility: http://appdb.winehq.org/objectManager.php?sClass=application&sTitle=Browse%20Applications&sOrderBy=appName&bAscending=true
VLC will be available in the repos

7.10 is end of life, dead and gone. It died April 10th 2009:
https://wiki.ubuntu.com/Releases

I suggest you upgrade to at least Hardy / Karmic / Lucid OR Maverick.

Because 7.1 Gutsy has died you may need to edit your /etc/apt/sources.list to contain the old out of date repository archived packages.
example

1. backup your sources.list
2. sudo gedit /etc/apt/sources.list
3. Replace the servers names with the following server
deb http://old-releases.ubuntu.com/ubuntu gutsy

example
deb http://old-releases.ubuntu.com/ubuntu gutsy main restricted universe multiverse

4. save the sources.list
5. sudo apt-get update
6. If this is successful you should now be able to install the packages you need through synaptic or apt.

see also http://ubuntuguide.org/wiki/Ubuntu:Edgy/Repositories#How_to_add_extra_repositories