First off, I want to say that if you are looking for keyword ranking through search engine optimization, noone can "guarantee" results due to the constant changes made by Google, Yahoo, etc... as well as changes made by other competitors that are trying to rank with those same keywords. Also, you should be made aware that some companies can guarantee you spots by using unethical techniques which can possibly get your sites banned from certain search engines like Yahoo, Google, AltaVista, and more.
It would be my recommendation to you that you also use search engine advertising (or pay per click ads) like you find on Google and through the Overture network. If you do decide to only use SEO, I would suggest it to be an ongoing project since most search engine algorythims are affected by how often a site is updated, and it makes it easier to stay ahead of any competitors.
If you are interested I would be willing to provide more information that can assist you in marketing your site and offer my services to you at a price that can be negotiated to fit your budget and the project.
Just to make you aware of my creditentials, I have been performing SEO, Web Design, and other forms of marketing (both on and offline) for several years now. My last job before going into business for myself was as Sr. SEO Officer of Data Resource Consulting where my skills were refined to make sure all my SEO and SEA practices are performed ethically.
I hope this information has been helpful.
Robert Carter
Xtreme Site Design