Concatenate and untar multiple backup files

[marmyx]

Hi
I've backup my entire clients with Plesk Backup splitted the file into 5
Now i have to concatenate the file to untar the backup using this http://kb.odin.com/en/1757
How can i concatenate the 5 files into 1?

i tried renaming the 5 files: mhtamboa.tar.gz.000 | mhtamboa.tar.gz.001 | mhtamboa.tar.gz.002 | mhtamboa.tar.gz.003 | mhtamboa.tar.gz.004

after that i used this:

cat mhtamboa.tar.gz* > mh.tar.gz

and after:

cat mh.tar.gz | munpack

but i receive this message

munpack: reading from standard input
Did not find anything to unpack from standard input

plese help me if you can, it's very important for my work

Thank you very much