With iTunes 8 Apple removed the ability to disable the store arrow links and the genre column through the preferences. I guess Apple are trying to keep the preference panel as easy as possible as well as use any given opportunity to direct users to the Store.
To disable the genre panel, open the terminal, enter this command:
defaults write com.apple.itunes show-genre-when-browsing -bool FALSE
and press enter.
To disable the the store arrow, open the terminal, enter this command:
defaults write com.apple.iTunes show-store-arrow-links -bool FALSE
and press enter.
You will need to restart iTunes if you had it running.
Repeat the above steps and replace the FALSE to TRUE to enable them again.