There is a lot of info already posted here about this type of arrangement, but I know the replies are generally the same and way over my head too.
Here is something I was told from one of the SEO's Boards and it helped me look at the subject from a prespective I could understand. These guys are Search Engines fire fighters :).
"Without seeing the site, I don't know how wise that is; but consider two potentially big disadvantages before you commit.
1. Google sees sub.domain.com (or www.sub.domain.com) as a completely separate site - as separate as chalk.com and cheese.com - so if they are really that different, why not give them individual domains.com, and avoid any visitor confusion?
2. With all your stuff on one site (domain.com/widget1/, domain.com/widget2/ etc), you will have X incoming links. Divide the site into (eg) 10 separate domains, and each one will have, on average X divided by 10 incoming links. That could destroy your Google placing at a stroke, with almost ten times the work to optimize ten sites instead of one.
These are potential down sides - you need to decide how much they will apply to your site(s).
With most service providers, you can have either sub.domain.com or www.sub.domain.com - but it is important to be consistent, or you'll further subdivide your links; sub.domain.com and www.sub.domain.com are separate domains in Google's eyes.