Downloading error

Hi, my MacBook Pro is almost 3 years old now and I am suddenly having an error when i try to download anything. It reads "[location] could not be saved because an unknown error occurred. Please try saving to a different location." I have always downloaded to my downloads folder but i tried changing it under my preferences to several other locations and nothing is working. I would be grateful for any advise! Thanks!
Currently running 10.5.8
Also note; i cannot download or instal (so i cant update anything)

Which browser are you using? Try cleaning the caches - browsing, download, etc. Repair permissions and then try again. You might want to download the free maintenance and cleanup tool "OnyX" from here. Run it in auto mode. It will clean the caches, repair permissions, and verify your hard drive.

Thank you very much, this problem was actually solved by someone on Mac Forums giving me the terminal comman to download google chrome where i was able to download safari afterward. I also realized that running Firefox in safe mode would probably do the trick. Thanks again, problem solved!