Buying sites and integrating into existing sites

Hi,

In order to expand my website I have considered purchasing other websites, it is my thought that I could purchase for example a site that was about soft furnishings and then put it on a sub domain of my current site. I will of course change the look of the old site to look exactly like my existing site.

I am concerned about the domain name though- If I was to purchase a website and domain that was receiving hits, then obviously I would want to point those people to the new location of the site, which will be the subdomain.

So there would be the soft_furnishing.mydomain and the url of the website, before I purchased it leading to the same pages, is this likely to get me in trouble with the search engines ?

Or is there a better way of doing this?

Thanks in advance