my macbook will not update or do installations can someone help?

You'll need to provide more information ... your system won't do a Software Update or your system won't download x update from y site or you can download an update but when you try to install it something (what) happens or ?

mine does the same kind of thing. its a 17" MBP 2.93gH from mid 2009. just wiped the HD and a new install of 10.6.3 from a cd from apple. direct internet connection or airport doesnt matter - get goo signal from both - download proceeds half way thru then i get a cannot save updates and will check again on the next update or theres a download error message and thats it. any thoughts