There are bus and train services to Mallaig, described here from Glasgow. You will get a sense of the scale of the journey from the car travel notes above. Timetable and fare information and online booking are available from Scotrail's website at http://www.scotrail.co.uk. Glasgow has two train stations, Glasgow Central and Glasgow Queen Street; trains to Fort William and on to Mallaig leave from Queen Street. Some train journeys from the south will take you to Glasgow Central, in which case you will have to make your way to Queen Street, just a five to ten minute walk from Central. There is also a free shuttle bus between the stations. From London Kings Cross, however, you can make a scheduled journey all the way to Mallaig, passing through Edinburgh and Glasgow Queen Street and avoiding any need to get through the streets of Glasgow.
If you have been staying in some other part of Glasgow the Underground train may be a convenient way to get to Queen Street. Buchanan Street underground station is immediately adjacent to Queen Street. Routes and timetables for train and underground journeys within Greater Glasgow are available from http://www.spt.co.uk. Note in particular the network summary map at http://www.spt.co.uk/Travel/SPT_network_2003.pdf.
It is possible to buy a ticket at Queen Street Station which combines the train to Mallaig and the Mallaig to Armadale ferry crossing. At time of writing the return train journey costs about £40, and the return ferry journey adds £4.80. The summer timetable is not available yet, but it appears at the moment that you will have to take the 0840 train from Queen Street - any later train will arrive after the last ferry departure at 1700. Contact us if you are arriving by this route: we may be able to pick people up, or at least coordinate shared taxi bookings for the last 3 km to SMO. This is probably the easiest train journey to SMO, although it is also possible to travel to Kyle of Lochalsh by train and conclude the journey by bus.
Bus services are operated from Buchanan Street bus station in Glasgow by Citylink (http://www.citylink.co.uk). The bus journey to Mallaig appears not to be much cheaper than the train but it is possible to buy a return ticket to 'Skye' for £20, provided you buy it at least five days before you wish to travel. This bus gets to Skye via Kyle of Lochalsh and the bridge - route and timetable at http://www.citylink.co.uk/route_glas2skye.htm. It heads for Uig in the north of Skye, from where one can take ferries to some of the outer islands. You should leave it just over the bridge, in Kyleakin, and connect to the bus to Armadale. The Armadale bus is operated by Rapson's who are also the bus company to use if you want to travel from Inverness. Their timetables are online at http://www.rapsons.co.uk/frameset.html (you want 'Area 6 - Skye and Lochalsh'). Alternatively, a taxi from Kyleakin to Sabhal Mor Ostaig will cost about £23.