I'm not modifying a single form, I'm looking to set the maxlength value for dozens of different products, all with different attributes that all have different maxlengths. Some products have multiple attributes, each with different maxlengths.

Even if I wrote some custom code to handle each product's attributes, I can't see how this would be a scalable solution. My client wants to be able to enter new products himself, and I can't predict what the maxlength fields will be for those products' attributes.

Yes, I've searched drupal.org, ubercart.org, and several Drupal books. I haven't found a tutorial that has helped me yet, I am hoping that somebody here with far more Drupal experience than I have will kindly direct me to a *specific* resource, as I've come up empty.

The contributed module you suggested is for Drupal 5 only, unfortunately.