'failure to mount' for software disk image?

You still need the .dmg on the end of the file name, although it should have kept that for you and just hidden it.

If you have a (2) named file, that indicates you also have one in the same folder without the (2) -- try opening the other one?

This sounds almost like you're attempting to open a filie that hasn't properly completed downloading.  You might want to delete all copies of Savosx72sa(whatever).dmg, and re-download from the site.

However, there are currently no pieces of malware for OS X that would slow your computer to a crawl, so you are not likely to be infected by a virus or other malware.  What version of OS X are you running?

Your issue is likely due to too many applications open, too little space on your hard disk, or corrupted cache files or permissions.  If you're running a recent version of OS X (10.5 or 10.6), I suggest you download and install AppleJack, reboot your computer into single user mode, and follow the instructions to fix hard drive issues, clean up permissions, clean bad prefs files and clear your cache files.