First, make sure you set the Sample to 'Direct'. This is done when you load an image into the texture dialog. After the loaded window appears in the Image Map dialog look at the options below the window. Find Sample and select 'Direct'. For more information check your Reference Manual on pg. R156.
Second, if you are using images that have a resolution setting above 72dpi save it as a TIFF rather than a PICT before loading it into your texture. A PICT file will be reduced to 72dpi, whereas a TIFF file will remain at the dpi setting it was originally set to.