What you're describing might be required for a report but would serve no purpose on a transaction such an invoice or sales order. This is because the software automatically wraps the text for you as you type your transactions and this wrapped text, regardless of length, will print on your forms.
The only potential problem with this is that if you convert a sales order into an invoice, then the extra comment text may not carry across unless you've linked the text to the product item. You can see if text is linked by adding the "S" (status) column to your transactions.
For information on this consult a tutorial such as:
http://www.capitaloffice.com.au/trainin ... singV8.pdf
Then go the section "Product Codes & Comments" which explains the difference between free floating and linked comment text. Or in other words, *how* you type your comments will determine if they carry through or not.