Dmoz are unlikely to use the title and description you submit anyway, the editors generally, well, edit it.
Just be guided by what is already in there, stick to a similar type of structure, length and wording and you have a better chance of the editing being minimal rather than a complete rewrite of what you entered.
For the title, the official site name is preferred and title should be a short and descriptive non-promotional title.
Bill's Specialty Widgets is superior to
Bill Sells Fantasmagorical Low Price Widgets
The description should describe the content of the site concisely and accurately and not be promotional in nature.
There is no limit of characters at DMOZ ;)
The title is (for commercial sites) the company name and nothing else, so the issue of limits doesn't arise.
If you think you're approaching a reasonable limit for a description, then go back and delete three-quarters of it, and you'll probably have something almost short enough to keep the editor from throwing it all out and starting from scratch.
Also, look at the category and it's listings you are going to submit to. You'll get a grasp of what is acceptable in most cases. By looking at the sites listed you will also see if they are similar to yours or if there may be a more appropriate category elsewhere. Remember, it's not where you want your site listed – it's where your site belongs that counts.
added: You should also read the category description (far right in same header/cell as search box) as it will often give you some insight on what is acceptable in the category and they often point you in the right-direction of similar categories your site may better suited to.
The website suggestion form says
|Keep the description of your site brief - no longer than 25-30 words. |
But don't assume that just because you picked your favorite 24.5 keywords, that the "description" will pass muster. It's always the editor's responsibility to write the description based on what's on the website. Your suggested description will serve you (and us!) best if it suggests what kind of site it is, and what kind of content the editor shouldn't accidentally overlook when reviewing the site.
And then assume not a word of it will survive the editing process. We'll make a silk purse out of your pig's ear, or sausage out of your prime loin chops -- useful or beautiful or not, you generally won't recognize the result.
I think there is a record somewhere of an ancient two thousand word submitted description that was basically the same 10 keywords repeated over and over again.
For the reviewing editor, after some hilarity, it was probably a very easy delete.