What do you think the chances of them reporting me to the RIAA are?
Who knows? There's just no way to tell what they will do. If you just have a couple of songs, and are not super active in the file sharing community, I doubt there would be much interest in pursuing anything -- but you just never know.
and what type of penalties would that cause?
Well, potentially you could be facing civil liability ranging from $750 per illegal song or movie up to $30,000 per illegal song or movie. I'm not aware of anyone actually going to trial on any of these RIAA lawsuits; most settle for amounts ranging from a few thousand on up to $20K or so.
How likely am I to face criminal liability for copyright infringement, as in has it happened in cases similiar to mine?
Like I noted earlier, criminal copyright infringement is pretty unusual, and requires more evidence than just a few songs on your computer. Usually criminal liability is limited to pretty serious pirates.
But again, you never know -- if they have some evidence of piracy on your part, I guess they could pursue this -- but again, if all you have is a couple of songs, its probably not likely to be a high priority. But, then again, you never know.
So do you think they will just end up returning my computer with no problems or do you think they are going to try to make a big deal out of it?
That will depend on what the local authorities want to do, no way to tell from here.
Bottom line is this: the chances of facing criminal sanctions for this are probably slim, so your probation shouldn't be affected (unless there are some terms of your probation that specifically cover this) -- but, then again, if the cops are realy out to get you, you never know.
As far as civil liability, well, that shouldn't impact your probation. Either way, at this point, you'll just have to sit and wait and see what happens. That's all you can do for now. If the cops come back with charges or something else, post back and maybe we can help -- but until something happens, all you can do is wait and see what they'll do.
And stay off the file sharing networks -- that's the best way to avoid any liability...