I don't *think* ram is the issue. I have 8GB installed on the system that I use to render our models, but I don't use all of it while Creo is rendering. It only uses about 2GB of RAM; however, it does take quite a bit of processing power. I've got a quad-core CPU @ 2.83GHz, and each core runs from 75% - 100% while rendering. Even if you have a less powerful computer though, it shouldn't crash, it should just take longer to render. I have heard there are some issues with Creo and Windows 7, though I haven't had many. At what point in the render does it lock up?
Also, we'd be happy to share some of our renders at full resolution if you'd like. We have many on our Facebook page,
here, and I would be happy to send some full-res versions around, just send me a message.