For a PC, Dell is ok as their configurations are always compatible with Windows. However you still have all the usual windows pain with them like viruses, spyware, bloatware, MS patches, rebuilds, buying or stealing software to do simple stuff etc. Also, I guess you'd get Vista with a Dell, and then you'll want to buy Windows 7 in a couple of months for $200.
Just buy a mac and be done with it. You won't regret it. Apple are basically giving their new OS to people that buy now as well.
You can see the
IMac buyers guide here.