Yo folks, didnt read it anywhere here ,so just for the wizzkids .. I use a Atari Trackball http://cgi.ebay.com/Atari-Trackball-NOS ... 5640505f98
(E-Bay link 29 March 2011) instead of an Atari mouse .. (since LONG way back in time )
A m8 of me converted the wiring about 20 years ago to work on my 260 ST ..
Never looked into it anyways, but if someone is interested in the wiring or so, I perhaps can open it up, or send it over..