hi guys,
i am new to HP unix , i am doing Solaris , i am just asking is there any thing like "bash" in hp unix including tab completion?

HPUX should have the posix shell with double esc working like tab in the bash shell.
but if you want to use bash, you could put it in your PATH so that it's available after login by giving the command 'bash'.

but the PATH contain the directories for you command, and i searched in my box i couldn't find any package or file with bash, do i need to download any files ?

Check if you have bash installed on server, if yes either set your default shell to bash or add bash command in .profile file in your home directory.
Another option is to use ksh shell with vi. This is not as easy as bash but vi commands can be used to complere,search previous commands, etc.
in your .profile or command prompt

ksh -o vi
ESC  |  will help complete the file names but will not do listing
Esc k   diskplay last command
/"command"  search ofr last execution of command, 'n' for next

how to check if bash installed? and how to install it ? from where ?

check:
# bash
ksh: bash: not found

how about:

which bash

# which bash
no bash in /opt/nokiaoss/platform/common/bin /opt/nokiaoss/irp/bin /opt/nokianms/bin /usr/sbin /usr/bin /usr/ccs/bin /usr/contrib/bin /opt/hparray/bin /opt/nettladm/bin /opt/upgrade/bin /opt/fcms/bin /opt/pd/bin /opt/resmon/bin /usr/bin/X11 /usr/contrib/bin/X11 /opt/graphics/common/bin /opt/perl/bin /opt/mx/bin /opt/hpnpl//bin /opt/perf/bin /opt/ignite/bin /opt/ldapux/bin /var/opt/netscape/servers/shared/bin /var/opt/netscape/servers/bin/slapd/server /var/opt/netscape/servers/bin /usr/sbin/diag/contrib /opt/ots/bin /opt/ots/lbin /usr/local/bin /opt/gnome/bin /opt/mozilla /sbin /usr/sbin /opt/oracle/product/9i/bin