I run Vista Ultimate at home and at work with no issues, 2GB RAM on a Core 2 Duo at work, 4GB at home, runs great. Yes, it has its quirks, but there are work-arounds and once you get used to it you'll probably like it. XP was the same way when it came out, way different than 95/98, and Vista is very different from XP. I wouldn't run it with less than 4GB, but don't bother running 64-bit unless you absolutely need more than 4GB RAM for an application. (32-bit operating systems have a physical memory limit of 4GB.)
At work we use nothing but IBM/Lenovo desktops and laptops. I touch them every day and love them, would highly recommend them to anyone. Their support is top notch as well, and I've dealt with many computer companies. Dell is the other recommendation I would make. I'd be weary of buying anything else.