Well, really 72 DPI as monitor resolution is only an approximation. It's the default that windows assumes, but it's not necessarily accurate.
DPI is really only a useful measurement when you're talking about printed output, where there is a direct correlation between the number of dots of printed output in an inch of paper.
Internally in ArtRage we dont even use DPI - everything is pixel-based. We only add the 72 DPI parameter when we export to Photoshop PSD.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"