I have been able to successfully install BT4 prefinal on both a d620 and a d630, both have dual wifi cards and 3 gig ram. Both wifi cards are successfully detected and operate properly, able to inject. Other than following the instructions in the "up and running with backtrack prefinal", I have ran into no issues so far on either laptop. Both were live cd boots followed by local harddrive installs.
On a further note I am also able to boot to usb with persistant changes on bt3 with both models and without persistant changes on usb bt4 pre.
I have not attempted persistant boot on usb yet for bt4 but should have time this weekend.