I read somewhere that entering an area (like a cave) locks the creatures within at your level. Is this right?

until the cell resets, yes

Before the game came out they said that each area had a 10 level range, i.e.: Level 1-10, or Level 11-20, or Level 21-30, etc. As you enter the area the level of the area locks at either your exact level, or the lowest or highest setting, depending on whether you are under or over the level ranges.

So someone level 34 walking into an area with a level range of 1-10 would lock at 10. If the same person walked into a area with a level range of 41-50 it would lock at 41. etc.

What this does is keeps some areas easy or hard no matter what your level is.

What I wanted to do was use the Oghma Infinium glitch to make sure the strongest enemies are in each area.

The Encounter Zones are talked about some in the Skyrim Fan Interview stickied right in this forum too.