Actually this IS quite common, heck it happens with montiors here at work, Intel Integrated & IBM 21" & 17", when changing your settings you will find a slight shift in many monitor/card combinations. Perhaps usually the shift is not small enough for you to notice, however it usually happens with CRTs.
Adjust your picture using the knobs/buttons on your monitor, and even a 15" should have no problem doing it. If your monitor is VERY old, the answer is simple, get a new monitor and run that hunk a' junk as a dual monitor crt.
Definitely sounds like a CRT issue, not a card issue.
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