Your internet plug-ins are suspect.
Go to Hard Disk/Library/Internet Plug-ins and drag the following to the desktop (but don't delete them yet):
Adobe PDF Viewer (check which version you have, it comes with Adobe Reader, the latest version of which is 9)
Netscape Plugin (Should be RealPlayer Plugin)
Restart Safari and see if that helped.
If it did, download and install Adobe Reader v.9 from
http://www.adobe.com/products/reader/
and RealPlayer 11 for Mac from:
http://www.versiontracker.com/dyn/moreinfo/macosx/15540
Once installed, perform this routine:
Repairing permissions is an important part of regular maintenance, and should always be carried out both before and after any software installation or update.
Go to Disk Utility (this is in your Utilities Folder in your Application folder) and click on the icon of your hard disk (not the one with all the numbers).
In First Aid, click on Repair Permissions.
This only takes a minute or two.
Background information here:
http://docs.info.apple.com/article.html?artnum=25751
and here:
http://docs.info.apple.com/article.html?artnum=302672
An article on troubleshooting Permissions can be found here:
http://support.apple.com/kb/HT2963
If you were having any serious problems with your Mac you might as well complete the exercise by repairing your hard disk as well. You cannot do this from the same start-up disk. Reboot from your install disk (holding down the C key). Once it opens, select your language, and then go to Disk Utility from the Utilities menu. Select your hard disk as before and click Repair.
Once that is complete reboot again from your usual start-up disk.
More useful reading here:
Resolve startup issues and perform disk maintenance with Disk Utility and fsck
http://support.apple.com/kb/TS1417
Post back with results!