1. Yes, any trunking scanner will allow you lock onto the talkgroup or talkgroups of your choosing.
2. Baltimore County is in fact in the process of converting to a digtal radio system. They are building out a series of new towers to support that system and the most recent information was that expected completion is fall of 2010. Once the changeover happens, analog scanners will no longer work. If I was purchasing a scanner now, I would go with a digital one so that I would be ready when the change over to digital happens late next year.
As far as which digital scanner, much depends on whether you want a portable or desktop/mobile and what features are important to you. The GRE PSR-500 or PSR-600 (
http://www.scannertainment.com/GREMain.aspx ) will be a bit less expensive and in many cases will provide a better sound on simulcast digital systems like Baltimore County is going to be using. The Uniden Bearcat BCD396XT or BCD996XT (
http://www.scannertainment.com/UnidenMain.aspx ) cost a bit more but have more features as well, like gps integration the ability to change display colors.
Feel free to call anytime to discuss your specific needs at 410-757-1676.