rpm：RPM should not be used directly install RPM packages, use Alien instead!

Do not install rpm in Debian (I don't mean flash-plugin, I mean rpm package management). Debian's package management system (which makes sure everything is installed properly and with no conflicts.) is dpkg and it also includes apt-get, Synaptic and aptitude that use dpkg. RPM will bypass dpkg, so you may cause serious damage to your system. 
If you need to install an rpm package, you must do it using the tool "alien".  It converts RPM packages to .deb and installs them properly through dpkg.

Code:

sudo apt-get install alien

To use alien:

Code:

sudo alien flash-plugin-10.0.15.3-release.i386.rpm

Then you can install it like this  (watch the .deb at the end) :

Code:

sudo dpkg -i flash-plugin-10.0.15.3-release.i386.deb

Or

Code:

sudo alien -i flash-plugin-10.0.15.3-release.i386.rpm

That will convert flash-plugin and install it.

A good reference guide for dpkg and apt-get  is here.