Congratulations on joining the Mac world and welcome to Ehmac!
After you installed these plugins, did you restart your machine? It could be something that simple. If they are still not working, try loading Safari and go to the help pull down menu. At the bottom is an option to show installed plugins. If they aren't showing up in the list, something went awry with the install process. Let me know what you discover and repost if this doesn't resolve anything. I'm sure other members can offer insight I haven't thus far. Good Luck!
Macbook: 2.16Core2Duo,4GbRAM,DL Superdrive, 120Gb HD
The Old Workhorse:G4 1.4Ghz,1.5Gb RAM,Radeon 8500,Airport,Sonnet ATA133 Card, USB 2.0, 250 Gig HD,LG & Pioneer DVD-R