Hi Mike,
I found this article online:
It's Not Too Late to Get Your Business on MySpace - Entrepreneur.com
I thought it was helpful, and to add to it... I would search under both Facebook and MySpace's policies and just double check everything to make sure you're following their rules.
Since your business is online, I'd suggest searching out professions and joining groups that have members that would probably be interested in your products. Never spam the groups or by sending messages, but instead contribute to those groups with your professional personality. Having your logo as your picture could help brand your site, but you could also add a personal touch by having a personal picture.
If you do any work with local charities or local businesses... or participate in any shows or events... post pictures and post it on your calendar on MySpace. Involve customers in the "behind the scenes". Keep a blog... It's ultimately your choice as to how personal or professional you want to take your business social site, but consider your customers or potential customers... and ask yourself if that personal touch means something to you...
Simply put, there's really not a rule as to what's most successful in marketing your business on social networking sites, but there are certainly a lot of ways you can be creative in your marketing process.
Social networking sites like MySpace and Facebook are one of many valuable tools in your marketing toolbox and online presence.
Good luck and let us know once you get it up and running.