|for starters, some specs would help. How old is 'old'? And what kind of graphics card/integated chip does it have?|
Depending on the type of the graphics card that is in the Thinkpad, it may not fill the screen.
My laptop, albeit rather new (2009), when running any kind of program with a lower resolution than the screen will not fill the screen. It keeps the aspect ration to prevent blur.
I'm not familiar with that system BUT if in your BioS it has something to change graphics card settings, look there. Look for settings that say 'Keep origonal aspect ratio' or 'Fill screen'.
Not everyone can decipher Klingon script...
chay' ta' SoH tlhe' vam Doch Daq