Hi Alain: I (and many others here as well) have IBM TravelStars installed on our Tyros and have not experienced any problems whatsoever. I own (and recommend) the 20 gigabyte IBM Travelstar 'model 40GN' (4200 RPM) which cost me $80 six months ago. There is also a faster (5400 RPM) more expensive model 40GNX version available, but on the Tyros, I'd doubt you'd notice any benefit of the extra cost.
This being said, IBM recently discontinued their Travelstar laptop hard drive line altogether, and subsequently, Hitachi 'took over' that Travelstar line, calling it the Hitachi Travelstar 'model 40GN' now. I concur with Micco that the Hitachi Travelstar is a good choice.
http://www.hgst.com/hdd/travel/tr40gn.htm The bottom line though, it that the Tyros will accept most any 'off the shelf' laptop hard drive which meets the following criteria:
2.5 IDE
Height 12.7 mm max
40 GB max
Scott