99 Legacy Outack - Belt Squealing - is it the timing belt?

Howdy All -

I'm the proud owner of a '99 Legacy Outback with just shy of 200K miles to its name.  By no means an avid mechanic, I've recently taken both an idealistic and pragmatic interest in doing as much of my own maintenance work on the old gal as possible – seems about time to finally learn something about how all of this stuff works!  :)  With that in mind, any insight y'all could lend would be greatly appreciated.

Upon starting my car, a belt will squeal for some time (the longest I've let it go unabated is about 20 seconds) unless I shift into reverse (which will cause the noise to cease).  Also, the check engine light came on recently, so I used the ole OBD to find that I have an issue with the knock sensor.  I popped the hood to visually inspect what belts I can see, but found none to appear frayed or overly worn.  Also, when I park the car after driving, I can smell something burning, but can't discern anything leaking.  Finally, I know I'm due to have the timing belt changed yet again (seeing as though the last time it was performed was at the 100K mark).  

I'm curious if this all indicates that it's my timing belt that is in serious need of changing, or if it might be another belt.  The reason I'm so keen on being able to differentiate this is because I'd like to be able to remedy the problem myself if it's a simple belt swap, but if it's the timing belt I need to get my car to my local mechanic (which requires a weekend trip back home).

Thanks in advance for any info you might be able to impart to this newbie -

Matthew