Video on a computer monitor is not always correct
Do some test editing and write a DVD-RW and play on a TV
I agree with John. Don't ever use the internal Premiere monitors for quality control. Always use a properly calibrated external TV of the best quality you can afford, preferably CRT.
What is the material that you are using, and how are you getting it into PrPro, Capture from tape, Import, etc.?
Im capturing miniDV,25fps I think. actually, it's a cinelook preset, using dvx100 from panasonic. which I think is 24p. Oh and in PAL due to me residing in the UK.
Capturing is a simple digital transfer of data. There is no modification of data during this transfer. However, since you are not sure what you have shot, 24P, 25P or 25i (you should check your camera for that) your best bet is to drop a captured clip on the New Item icon in the project panel to create a new sequence with the proper settings.
If you still have the idea that the exposure is off, this simply means that your monitor is not properly calibrated and unsuitable for quality checking.