There's one more thing that factors in (before Radek jumps in to correct me again [img]smile.gif[/img] ) -- your actual level.
You can learn spells at half your actual level, rounded down, as well. So your level 11 ranger can learn up to level 5 in non-native spell schools (everything but Vine), and up to level 7 in vine. In both groups, her spell school level also counts -- at full value in vine, and at half value (rounded down) in the others.
If it makes you feel better, it's only frustrating in your first game.... [img]smile.gif[/img]
And to emphasize something that bsftcs said in passing, be sure to learn fletchery before you change classes from Ranger. You'll need to be level 5 in the warrior guild (which means you'll have to pass the salads in Ishad N'ha), but it will be well worth it...