If you wanted to know how, it can be done in a couple of ways.
The first one is just replace ../styles/prosilver/imageset/site_logo.gif with a different logo (although if size is different then second method also need to be used to change the dimensions).
The second method is to upload a logo into the directory:
../styles/prosilver/imageset
Then go into the ACP, and go to:
Styles >> Imagesets
Click on "Edit" next to prosilver. Then click "Select" next to "Select image: Main logo". Locate the new logo etc.
No, it can be changed, but I don't really know how, and I trully don't have the time, since we have to change a lot more than just the logo.
Understandable - a complete custom style would be very time consuming!!
Arite.