Online Stores & not hurting my SEO for Google

[kidder]

One of our sites is a clean information based forum using adsense only as the revenue model. I wanted to introduce some products to my users but I am concerned that it may have a negative effect on my organic search rankings if it is not done correctly. I wanted to get some feedback on what is the best practice in terms of SEO - Do I create a directory on the main domain for the store or am I better to use a sub domain? I don't need these pages to rank in search results so is it just a matter of locking the bots out of that directory with robots.txt?

[fishfinger]

If you don't want the pages to rank and are going to block them then it doesn't really matter how you do it - use the most hideous urls and bloated code imaginable.

Do you not want to get traffic directly to the product pages because you are going to use a feed for the products and can't make sure that your pages will be unique?

If you can control product descriptions etc then I'd make the pages spiderable myself. I don't know what your site looks like but I would

(a) set the shop up on shop.domain.com
(b) have featured product links on your info pages - just the pic, price, snippet (using text not used on the product page) etc with BUY NOW or MORE INFO linking through to the actual product pages in your shop.
(c) add a sitewide link to the shop subdomain.

[kidder]

Thanks for that advice - I was leaning to the subdomain idea in which case I would make the pages search friendly (we already have 300k in the index on the main site). Linking to the subdomain as you have said via 1 sitewide link and maybe using a java script to rotate product "image" links through the header to keep things mixed up and fresh on each page load.

Does anyone else see any obvious seo flaws in my plan?

[kidder]

One more question here - when setting up the subdomain does it make much difference if you go with dedicated or shared IP on the sub?