wow, that's not good.
when you run apt-get update i guess it doesn't do anything just says "Reading package lists... Done"
here's a sample of /etc/apt/sources.list + the 2 required repositories
Code:
# Find more repositories here: http://www.apt-get.org
# CD images - etch installer http://www.debian.org/devel/debian-installer/
# deb cdrom:[Debian GNU/Linux 4.0 r0 _Etch_ - Official i386 CD Binary-1 20070407-11:55]/ etch contrib main
# regular updates for etch
deb http://ftp.debian.org/debian/ etch main contrib non-free
deb-src http://ftp.debian.org/debian/ etch main contrib non-free
# security updates for etch
deb http://security.debian.org/ etch/updates main contrib non-free
deb-src http://security.debian.org/ etch/updates main contrib non-free
# multimedia Christian Marillat (was: ftp.nerim.net)
deb http://www.debian-multimedia.org etch main
deb-src http://www.debian-multimedia.org etch main
# unofficial http://www.debian-unofficial.org
deb http://ftp.debian-unofficial.org/debian etch main contrib non-free restricted
deb-src http://ftp.debian-unofficial.org/debian etch main contrib non-free restricted
# stable
deb http://ftp.de.debian.org/debian/ lenny main contrib non-free
deb http://security.debian.org/ lenny/updates main contrib non-free
just "pico /etc/apt/sources.list" copy+paste the above code, save the file and run apt-get update. now you should be able to install ispcp.