Your first two commands are not necessary. You already have apt installed, and any necessary updates will happen automatically.
In order to get to Sid (Unstable), Edit the repo lines in your /etc/apt/sources.list file to look like this:
deb http://ftp.de.debian.org/debian/ unstable main contrib non-free
deb-src http://ftp.de.debian.org/debian/ unstable main contrib non-free
# apt-get update
# apt-get dist-upgrade
I suggest after that, you should change your sources.list back to testing, and, in the future, go to Sid only for packages that you specifically want. That way, you also get to take advantage of the recent installation of security updates for Testing.
My sources list looks like this:
# deb cdrom:[Debian GNU/Linux testing _Etch_ - Official Snapshot amd64 Binary-1 (20060327)]/ etch main
deb http://mirror.espri.arizona.edu/debian-amd64/debian/ testing main contrib non-free
deb-src http://mirror.espri.arizona.edu/debian-amd64/debian/ testing main contrib non-free
#deb http://mirror.espri.arizona.edu/debian-amd64/debian/ unstable main contrib non-free
#deb-src http://mirror.espri.arizona.edu/debian-amd64/debian/ unstable main contrib non-free
deb http://secure-testing.debian.net/debian-secure-testing testing/security-updates main contrib non-free
I do regular dist-upgrades to pick up any new packages that have moved to testing, then whenever I want a package from SID, I change the comments to go there for a specific package, then set them back to testing. Each time the sources.list is changed, you do # apt-get update, and then carry on.
The initial # apt-get dist-upgrade to Sid may fix your mouse problem. If it doesn't, that gives you a first area to work in.