Argh, why didn't you say so before? >
When you said you had this problem w/ CS 1.6, I naturally assumed that you had a regular Steam CS 1.6.
Of course, some dubious ripped illegal version you got from some bloke on a LAN party is not the ideal platform for anything.
Just FYI: There are some Steam-free CS 1.6 versions floating around on the net which seem to be quite ok, but with inofficial software, it's always a bit of a lottery. Since I dumped Steam and don't play CS online any longer, I once tested one of these, and it worked perfectly with PB 2.6mm. But if you want to play at home or on LAN with bots, you can stick to CS 1.5 as well - it runs perfectly with PB 2.6mm, and besides it's perfectly legal.