To use Paint as Default viewer:
Right-click on file with JPG, JPEG, OR GIF extension....Click "Open With..."...Click "Choose Program"....Select Paint from the list, and then click the checkbox that says "Always use the selected program to open this type of file"
To add icon to your desktop:
Go to C:\Windows\System32. Right click on mspaint.exe. Select "Create Shortcut". Take teh shortcut icon that was created in the same folder and drag it to your desktop.
excellent...i'd run some sort of virus/anti-spyware scan at this point....i can't think of another reason beside software as to why this folder's attributes would have been changed