Granted you shouldn't have to block them, but the problem is that like children at times their search engine bots misbehave. They might only misbehave for a relative short period of time. You have a couple of options available to you:
1. Block them until they stop visting your site so often ("ignore them until they shut up")
2. Add robots.txt rules to slow them down ("ask them to stop")
3. Throw money at the problem and move to dedicated hosting ("give in to every demand")
4. Find out why they want to visit so often in order to prevent it from happening
Exactly! Just like pie (server resources), there's only so much to go around - and with shared hosting, you are sharing that pie with other people. DreamHost has told you that your site is trying to hog the pie. You can either stop your site from hogging the pie, or get a pie all to yourself by finding a dedicated hosting service.
Of course its easy to blame somebody else here, but you do have to realize that you are responsible for your web site, not DreamHost. If the problem is indeed cause by high traffic, then they can only suggest that you pay more for a virtual private server or find someone else to host your sites. You can allow DreamHost some time to make sure their hardware and the software they provided is not at fault, but if they are not in the wrong, it is ultimately up to you to fix your site or determine what your site needs in order to run smoothly.
Now, if you don't want to have to block any visitors, you might want to start learning how much memory your site needs, because DreamHost has told you it is using too much. You might want to hire a PHP developer if you are not familiar with web technologies.
Another problem is that your robots.txt file is incorrectly formatted as rich text (RTF)
Another problem is that "globalmotors.net" is redirected to "www.globalmotors.net" but the links to all your images are to "globalmotors.net". This means the browser hits your web site twice for each image - (your access.log must be gigantic as a result)
You have 1,140 results in Google and they all seemed to have been cached in the past week.