Normal maps are pretty cool, too.
You'll probably know that more polygons take longer to render than less polygons, and this affects your frame rate.
A normal map is a 'map' of how light reflects off a high-poly model, that can be then applied to a lower-poly model to make it look a lot like the high-poly model, whilst not taking that much longer to render than the low-poly model alone.
Only problem is they take up megabytes and megabytes of video memory, and the only suitable compression available on-card is manafacturer specific; Because it's not a normal texture, normal compression (JPEGs, etc.) produce these huge ugly artefacts upon your model.
Part of the 'Emergency Response Noob Shooting Team' :: Feel free to add me to MSN, but don't expect any big favours.
I AM _NOT_ A MOD, I AM ONLY HUMAN (although I fly in my spare time).