Lke Knoppix before it another method for seeing onto a drive if connected correctly while partition information is somehow lost making it invisible to Window I grab a live for cd Linux distro like the latest releases of ubuntu 7.10 and now 8.04 to see data can be rescued while booting up with a live cd.
The image here shows how accessible even an external usb drive is while booted live by that method for copying files. It can save a world of hurt to get at files, back them up, and then even repartition and reformat the problem drive to recopy things back later.
First recheck the jumper setting if an ide drive to see if that is set for the position on the cable if the drive is an ide type. If set to master while you plugged it in on the middle connector the slave or cable select jumper position would then ne needed. Check the power plug to make sure you didn't forget that and if sata then assume possible loss of partition info.
Once you are in the Administrative Tools>Computer Management section that Makaveli213 posted there double click on the "storage" item seen in the right window to open that up to see the Disk Management tool and click on that to bring up the small screen with all drives installed seen there.