You can take the KMB bus no.961, from 山景總站 then it pass by 屯門市中心 and the end station is 灣仔會展巴士總站. (Bus fare $18.2)
http://www.kmb.hk/chinese.php?page=search&prog=route_stops.php&route_no=961&bound=1&select_from=13A&select_to=16B&scenario=1&stop_from=&stop_to=
Another bus is KMB no.960, from 建生總站 then it pass by 屯門市中心 and the end station is 灣仔碼頭總站, which is very near to the 灣仔會展 also. (Bus fare $18.2)
Of course 961 is more direct la!
If you want it to be cheaper, you can take the bus from Tuen Mun to Tsim Sha Tsui first then take the ferry to WanChai.
There are Buses no. 63X, 260A, 260B, 260P, 260X, 261B and 267S can go from Tuen Mun to Tsim Sha Tsui...(Bus fare about $12 to $13) then take the Ferry at fare of $2.2...you can walk to 灣仔會展 then, this way is cheaper.
2007-07-20 13:13:57 補充:
**************************************************************************************************************************屯門(屯門市中心)搭961到會展 la!!!