Is this what you mean,

PS/2 to USB adapter

Here is a link that might be useful: PS/2 to USB adapter

no the one mentioned is the ancient type with 9pin d connection.
this would allow you to use the 9PinD on the PS/2 or 9pin port on the pc.
Serial to PS/2 Mouse adapter connector pinout

but that is assuming you could ever find such an adapter and the price, plus would the old mouse even work on the windows 7 OS. This would be why I say that
Using 6-PIN Mini-DIN Connector for 9-PIN Serial Port

this may or may not work no clue
MOUSE ADAPTER - 6 PIN MINI-DIN - FEMALE - 9 PIN D-

contour makes a current 3 button mouse but has a ball on the side, but I think there is an option to get it with out the ball
http://ergo.contourdesign.com/

you know where I would try, I would hit some of the local fixit computer repair shops I know the one I used to go to had baskets of that old stuff that he offered to give away because he had no use for it.

this is what you want, it is an old logitec mouse man mouse, I had one just like it, may still have it somewhere or I thew it out when I moved.
{{gwi:1439175}}

well I did a search for logitech mouseman on ebay and low and behold they have several listed, some ps/2 some with the same connector you have and even a wireless one with the receiver.

Here is a link that might be useful: ebay search

Thank you, ravencajun and zep, for your input ! :-)

1. My apologies for this becoming another thread. I intended for my first post above to be a reply to my other "two mice" thread, but for some reason it didn't come out that way. :-(

2. I'm not sure if any of your suggested adapters will work, ravencajun, but I'll certainly check them out more thoroughly.

3. The Contour Mouse looks interesting, but it's obviously way overpriced for my particular needs at the moment.

I'll keep investigating.

Who knows ?.... My next post here may, in fact, be made with the help of a wow pen mouse after all. ;-)

Thanks again.

Thank you for the ebay link, ravencajun ! I didn't see it when I posted my comment above.

Well, with all these options to choose from, I certainly have a lot of 'mousework' to do today. ;-)

Thanks again !

I saw on that ebay link a brand new still in the box logitech laptop mouse with the 3 buttons listed it mentions PS/2 which should be fine most computers have those connectors and an adapter for ps/2 to usb are very easy to find and cheap, most any pc store carries them. I picked up a few at Fry's a few years ago.