Unable to install anything on MBP

Recently realized that my MBP (10.6.7) keeps getting the installation failed error message every time I try to install from a .mpkg. I also get the same error when I try to update to 10.6.8 (via Software Update AND the combo update downloaded directly from the Apple website). I also can't install any apps from the app store.

I've already looked extensively into the issue to no avail. I've tried to epair disk permissions from the Snow Leopard DVD. Someone told me my downloads were getting corrupted so I've also re-downloaded files (in safe mode, after rebooting router and modem, ethernet directly to router then modem, on another wifi network).

Any help would be appreciated.

Have you attempted to login to another untouched user account on the same machine to see if installing apps/updates works on the other account?

How much free space on the hard drive, and if at least 15-20% of total, boot from your Snow Leopard disc and run Repair Disk and see what is reported.

Tried both these. Still no dice. I tried uninstalling and reinstalling a software I still had the .pkg file for and it installed fine. So this leads me to believe that my downloads are getting corrupt. But again, I've tried Software Update on more than one networks so it seems like my downloads are getting corrupt no matter what network I'm on.

What browser are you using to download the packages/apps?

Try switching browsers.

Just tried that with no luck. I think I might reinstall the OS and see if that works out.

Are you getting an error code or something else beyond "installation failed"? It's likely that this can be fixed without having to do a re-install.

Nope, just the same error code "Installation failed please contact your software manufacturer" or something like that. I'll attach the error messages found on Console for when I try to update, when I try to install from the App Store, and when I try to install from Installer.app

Do you have ANY KIND WHATSOEVER of an "anti-virus" installed?

Good news. My problems seem to be all fixed. I reinstalled Snow Leopard and it went back to 10.6.0. After that I was able to install the 10.6.8 combo update and finally bumped it up to Mountain Lion. The software I was initially trying to install works now as well. Thanks for the input.

Glad that worked out for you. For the benefit of future readers of this thread did you by chance have one of those programs installed that offers to speed up your downloads?

Nope, nothing like that.