First you will need a PS/2-to-USB adapter. The active type, that has some electronics inside it. They should be widely available to buy new - every computer store should have them.
There are also small cheap adapters that don't work for this - those were meant for keyboards and mice that support both protocols over the same cable, and are completely wrong. You can usually tell the two kinds apart by price and size if the catalogue descriptions are lacking in info.
Then, if you can fit the adapter inside, you would have some crimping and/or soldering to do.
There are panel-mounted mini-USB plugs available. Panel-mounted micro-USB plugs are very difficult to find though.
You could look in the
Making stuff together subforum for threads of other people's conversions. This thread should also have been posted there btw.
The BTC 5139 is a nice keyboard for a rubber dome, by the way. The keycaps are mostly (but not completely) compatible with the mechanical Cherry MX switch.
I got two BTC 5140 - one I took apart and used the case to build a new keyboard and the keycaps on another. The other one I liked so much that I keep around and use now and then.
