You may need to see your video memory size on your linux computer. Here I will show you how to do it from command line. All you need to complete the mission is lspci command.
On Ubuntu 9.10 you find already installed dictionary, but to use the dictionary you need to go online. Without the internet connection you cannot use the dictionary. Then you need an offline dictionary so you can use have a dictionary even you are not online.
The dictionary that I will recommend to you is stardict. Here I will show you the steps to install it. First you need to install the stardict from the repository.