I have an old last version EMAC 1.42GH running 10.5.8 can't locate bluetooth capability in preferences need assist

Bluetooth hardware was a option in that model. It is rather rare as there were fewer BT devices in 2005 that justified a special order.

I have never seem the Apple parts that givbe Bluetooth advertised on the used part market.

You can get an external BT adapto that fits a USB port:

http://eshop.macsales.com/item/IOGear/GBU321/

That will let the mouse work on a basic level (clicking and selecting) but the eMac is too old to suport OS 10.6, required to get all the cool Magic Mouse capabilities (scrolling, gestures, special taps) working. Basically you'd go to the trouble of buying the adaptor and setting it up, and still end up with no more functionality than a $10 wired mouse will give.

Thanks for the greenie! We have the same model eMac here and it has been a rock-solid workhorse for 11+ years. Because it worked so well, my wife used it long beyond its "expiration date" and, when we upgraded her to a new iMac last year, I kept the eMac 1.42 to go in my shop. Too good to scrap (also upgraded to 2GB RAM like yours.)