Boot camp first, then Parallels?

My company is considering replacing our PCs with iMacs, but because of the nature of our business we need windows software, mac versions are simply not available.

Which leads to either boot camp or parallels.

I have read somewhere that parallels can 'pick up' a previous boot camp partition, and basically run that installation of windows inside a parallels window inside leopard. Is this a better way to go that simply bypassing boot camp and going striaght for parallels?

Will this require a re-activation in parallels of the oem copy of windows that we would install and activate in boot camp?

Another related question, can we use our existing oem XP pro licences in boot camp/parallels, or will they stay tied to the old PCs they came from and essentially 'die' when the PCs are scrapped?

Regards, Chris.