It's funny that you have this issue....I'm not sure of your circumstances, but I have two hardrives connected....and for some reason, with W7 RC (7100), it will not "detect" my second drive.
So I right-click on Computer, -> Manage, -> Disk Management....low and behold, my second drive is there but it's not been assigned a drive letter....so the moment you select a letter for it, it'll be present.
....not sure if this is the same issue you have, but hope it helps.