There's a wealth of information on the internet about sensor cleaning, Paul - even BF has a lot of helpful stuff.
Personally, I wouldn't go
near the inside of my camera with tinned compressed air. OK in theory, but it's
essential that you keep the aerosol completely level to ensure you don't splatter the innards of the camera with liquid propellant.
A Giotto Rocket blower is a much better idea, IMHO. Hold the camera upside down with the lens off and the mirror up and give it a few squirts, and you might shift the offending muck.
If that doesn't work, I'd suggest the Copperhill Sensor Sweep brush - it works really well to dislodge muck that isn't stuck to the sensor, using static electricity to lift the dust.
Failing that, you're into Pec-pad/spatula/Eclipse fluid territory - "wet" cleaning - but it's straightforward enough if you follow the instructions.
Suggested reading:
http://www.luminous-landscape.com/essays/sensor-cleaning.shtml
http://www.pbase.com/copperhill/ccd_cleaning
http://www.earthboundlight.com/phototips/where-is-that-dust.html