I'm lazy(and I do linux server administration, too lol) when it comes to commands and weird file names. I like to use wildcards...so what you got is the right syntax, but you may be missing a character, try this:

sudo dpkg --install /media/mmc1/libcap*.deb
sudo dpkg --install /media/mmc1/avahi*.deb

'sudo' is to make sure it's being done as root. That package you have to gain root might not kep it in the xterminal. FYI, to become root in xterm, I use 'sudo gainroot'. The default root password is 'rootme'.

Hope this gets it installed for you!