Photographing Ice Hockey: K-x vs. K20D

I have been reading the recent K-7 thread with great interest. I have a K20D. From September 2009-March 2010 I took at least 10,000 exposures at my son's hockey games, shooting from either a penalty box or behind the bench, using a DA 50-135 2.8, shooting with an aperature priority setting of

Mid-range Zooms

Can anyone discuss the relative merits of these three Pentax AF zooms: +28-105mm 3.2-4.5 +28-105mm 4-5.6 +24-90mm 3.5-4.5 Thanks much, Robert __ Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now. http://mailplus.yahoo.com

MZ-S Focus Lock

I feel like a dummy asking this question, but: I just bought a MZ-S and I'll be damned if I can get the focus lock to work when recomposing the frame. Has anyone experienced the same problem, and if so, any tips? Thanks much. Robert __ Do you