yum help...........
 

i am unable to install any package using yum.....
is there any method to reinstall yum....
also when ever i boot into my system i get the packagekit error message...

When you are asking for help you need to provide at least some information. What distro, version, and arch are you running? What is the exact error yum is giving you? Same for packagkit. Without this type of information there is really no way for us to assist you.

ok my distro is fedora 9
the error that i get when i update using yum is

[root@localhost ~]# yum update
Loaded plugins: refresh-packagekit
primary.sqlite.bz2 | 276 kB 00:15
http://fedora.tu-chemnitz.de/pub/lin...ry.sqlite.bz2: [Errno -3] Error performing checksum
Trying other mirror.

i have done yum clean all and also reinstalled yum but i still get the same error....

It looks like you have a bad repo. Since that address is incomplete it is hard to tell. You also did not give your arch (32bit/64bit/other).

Post back the results of yum repolist.

You can download the yum RPM package from rpmfind.net or some similar site and install/update directly with rpm (package name dotted out where version number and hardware type is shown):
rpm -Uvh yum-...fc9...-rpm

You can also use the Fedora Add/Remove software tool, that seems to have access to different repo data.

Rpm can be option when there is no yum configured. It will have lot of dependency issues and hence yum is preferred. Add/Remove programs tool most probably uses same repositories as yum. So if there is issue with the repo then it will most likely not work.