Everyone has given some great feedback! I think you hit a great avenue by targeting "P/T Administrative". I look for that, too, when browsing through Craigslist and some other job boards. I think it can be a terrific way to introduce your business and give them another option they might not have known or entertained.
Make sure to REALLY promote your business AS a business and NOT an employee - remember that most likely that is what they are looking for. Give them as much info upfront as you can that will spark their interest as well as make them contact you.
I would not give them my personal resume, but an outline of my experiences and knowledge.
If I am in the process of doing a mailing, I sometimes go through the postings and get their mailing address to send them a mailing, too. Sometimes the business name is right there and other times the company name is in with an email address. A little research on the internet and wa-la - got the addy!

Of course, sometimes it doesn't work that easily, but I will give it a try.
Anyway....yes! I think the attempt is worth it.
Good luck!