I have 2.1 installed right now. It runs fine and all the new features sound great, however the simple fact is that I don't get nearly the same amount of good hits per search as I used to with version 1.7b.

Even with six Ultrapeer connections I get far fewer results. Usually if I want a fairly recent and popular mp3 I can find it, but If I want something a little bit more obscure then 2.1 lets me down.

Can 1.7b and 2.1 be installed together? How about run together (so I can compare search results)?

Yes you can install them together .
And run them side-by side .
Aslong as you make sure they won't connect to eachother .
Put the adress 127.0.0.1 in the "forbidden IP's " list .

BTW : 2.1.1 adresses these problems , should be fixed .
So download 2.1.2 and it should give about the same results as 1.7 again .