Isn't there a way to define the number of characters a cell will
allow? Our operating system has fields that have defined character
lengths, we need the form our folks fill out to have the same limits.

One way with Excel 2003 is:
Data Validation Settings
Allow: Text length : Maximum
Data: Less than or equal to

Caution: while this prevents typing in too much text, it doesn't prevent
pasting it in.