Hi,
If the tarball is a source tarball you just do :
$ cd your_download_directory
$ tar jxvf net-tools-1.60.tar.bz2
$ cd net-tools-1.60
For the srpm, you do :
# rpm -Uvh net-tools*.src.rpm
# cd /usr/src/Mandrake/SOURCES
You will probably then just find a similar tarball of the source there which you'd need to unpack similarly to the above (use 'zxvf' for a tar.gz instead of 'jxvf').
Normally when you build the rpm from source it will unpack on the fly (into /usr/src/Mandrake/BUILD) so thats why the source is not unpacked when you install the source rpm.
If you are interested, to build the binary rpm you do :
# cd /usr/src/Mandrake/SPECS
# rpm -bb --target=i686 net-tools.spec
When its finished the rpm will be in :
/usr/src/Mandrake/RPMS/i686
and you can install it in the usual way.
Hope this helps