Usually when you first launch a legal web site, your going to do a more aggressive Pay per click campaign at Overture and Google adwords because it takes some time to get good organic or free listings, especially at Google. Over time you can draw back on your PPC campaigns once your organic listings come in, but its usually best if you can have both going.
This way you get the most exposure on the search engine page. When you have your firm listed in the organic listings on the left side and then also the sponsored listings on the right side, it gives you a better chance of someone clicking on your site and finding your firm.
An example of a law firm that has dual exposure at Google is The Law Offices of Don Thompson. If you type in the search of Chicago Probate at Google, his site comes up #1 in the organic listings on the left side, then the same site comes up on the right side under "sponsored listings".
Sometimes it might not make as much as sense to bid on keywords that are very expensive, especially if your already coming up in the free organic listings but if the pay per click keyword is less then 50 cents per click, then I would suggest it.
Getting listed in the PPC engines is easy, the real trick is getting your law firms site in the top 10 in the organic listings. We have helped many lawyers achieve this and as a result they have gotten new business and many new clients. Contact us if we can help your law firm succeed on the Internet.