This is worth a look, & bookmarking, if your needing to clean your sensor...

http://www.cleaningdigitalcameras.com/index.html

for what it costs, get a Nikon or Canon, etc authorised specialist to do it, not sure if Calumet and Jessops do it, but the risk of damaging the CMOS/CCD sensor, or the low pass filter if fitted ( for sensor cleaning ) just isn't worth the chance...

chances are the dirt is on the butt of your lens or in the viewfinder... it's not as common to get it on the sensor itself...