How to integrate classified ad script to website?

Hello, I have been researching for a few days and still can't figure the direction to go. I have a website that I want to make into a site where users can go in, sign up for a small monthly fee, to list their business on my site - this is geographically based and is for a service in my city.

So I asked on here a few weeks ago and was told there are a few plug ins that I could get for "classified ads" that would do what I want to do. I checked them out and found a great one that has themes for a price, but when I asked about editing the themes since I already have a look to my website that I want to keep, I was told that there are no tutorials on how to do that. I don't want to pay for a plug in and then realize that I can't customize it because I don't know how to do it (usually I work primarily in Artisteer)

So I checked Noah's classifieds since they are compatible with Wordpress but I tried to install it in fantastico and it said that I couldn't have more than one "script" in the main directory. What does that mean?

I'm at a loss. I'm thinking maybe I should just pay someone to design the site! I know it will be a good money maker... but my husband is layed off and I don't have a lot of up front cash so we're trying to research this together to pull it off rather than paying someone to design it.

Can anyone help? Could I make this work with Noah through fantastico, should I buy the $199 version of Noah or is there something else I could use?
Thanks!