You'll need a built-in firewire interface (rare) or pcmcia card (probably your best bet) in order to use your firewire drive on a pc laptop.
Just about any typical standard pc laptop's cpu would be fast enough nowadays.
Ram....as much as you can afford/squeeze into the thing.
PTLE on pc comes with the same plugins as the mac version does....except for maybe the special bundles.... compressor digiverb and eq plugins are standard. I prefer the plugins from Waves, myself tho.
www.waves.com
As for how much you need to spend....that all depends on which manufacturer you buy from. I prefer IBM thinkpads...but they're typically more expensive for a laptop with comparable features from say Sony or Dell, etc. I wish I could afford a new laptop and a digi002R.....that'd make my travelling studio life much easier.. =)