The acer aspire 5100 laptop runs on a AMD 64bit cpu, and because of that some software you may normally find on a i386 distribution is not ported fully into the 64bit versions of ubuntu. Such as the case for flash. In 7.04 version flash wasnt available easily and its hard to surf with firefox when so many sites now use flash in their programming.

To install flash download the flash_64_bit.tar.gz file and extract the contents into a folder, close all web browsers (VERY IMPORTANT) and from a terminal navigate into the folder and type the following commands

chmod +x GetFlash to make the script executable

./GetFlash to execute the file

Follow along any prompts you may receive and when the installation has stopped you should have flash up and running. If not try a reboot and check again.