If an animal form is assumed, or monster, look up the creature in your Creatures and Monsters or whatever. Look at the level listed for the creature. The abilities listed are the abilities possed at that level. If the PC is higher or lower than that level, adjust his hits/OB's?etc according to the creature rules in the front of the book. In addition, there is a level variable letter. Look at the letters colum abd see just how much higher level the creature can be. Add the max additional levels to its base level and you have the max level for the creature. This max isn't the max level of the PC, but can be used to impose the creatures max OB's, hits, poison levels, spell abilities, etc.
lynn