Most of my comments are about content and getting the message across. I think you have a good start but here are a few things that I think would help bring your message out.
Make some of the text larger, its a bit small particularly on the home page. You want to feature your site, not make it too hard to read what it is. Actually maybe turn that top paragraph into a short bullet list or something more visually appealing. I didn't want to read it, but I needed something to understand what your service is and can do for me.
The login/register option is a bit confusing. It took me a second to think "Do I NEED to register, or can I just search before I register?" which means that other people will probably think similarly. You have your login/register options very large, but the actual search feature is kind of tucked away at the bottom. I would say put that up top! People love to search before they commit to a site.
Its also unclear about the landlords ability to post. Perhaps it would make sense to have a section which has "Find a room" and another that says "Rent a room" or some combination which makes sense.
The better you can make the site over simplified on the home page, the better I believe. If you are expecting that people will be posting rooms/houses for rent, then make sure you provide Renters with enough incentive to post and not just market to the Rentees.
The login should be somewhere on top or left, it seems akwardly sitting on the middle bottom. You have plenty of real estate (pun intended) to work with on the page, so get some of these various sections pulled apart for clarity and to improve the overall message.
jeremy - gnomeontherun
Educated questions often get educated answers, and simple questions often get simple answers.