Assuming it has threads inside - of course it does - you could outfit it with a Shimano Octalink.
This is, of course, a possibility, but you can get a square taper bottom bracket that will work just fine with your current crankset. The important statistics are the width of your bb shell (either 68 or 73), and the length of the spindle. If you want to swap it yourself, you'll need a bottom bracket tool, and you'll need to read up on extracting the fixed cup of your current bottom bracket.
As far as which Shimano BB to buy, I'd put my vote in for the UN - 53/54 level. The 26-level is lower-quality, and I've had them die on me. The 54-level lasts forever.
Take your current spindle to the LBS when you go to buy a new one, and they can match it up.