This might help you, Ihave a 500Gig drive that's about half full and I was concerned about it for the same reasons. This may be overkill, but it's guaranteed to be 100% safe.
I had 2 WD Raptors as my windows drives in XP, C: for windows, programs etc and D: for the page file and 'working' data. My 500Gig drive (E
I use for long term mass storage - vids, mp3, photos and so on.
In XP I copied the 40Gigs off my drive D: to a new directory on E: called, er, "Drive D". I then unplugged the SATA cables from Drive C: (after switching off, obviously) and E:, and installed Win 7 directly from the CD on to the now empty 2nd raptor, my old drive D:, although Win 7 called it C: ofcourse, as it was the only drive in the system.
I then put everything back (i.e. reconnected) and I can now boot into XP or Win 7 simply by using the boot option in the BIOS on the first screeen (usually accessed by pressing ESC.) In both cases the Windows drive comes up as C: and the other Raptor as D:, drive E: is still drive E:.
Now in either XP or Win 7 I can access the other Raptor and all the files (makes carying your XP data forward a piece of cake) and the 500Gig drive too and nothing's been lost.
I haven't used easy transfer, nor any external storage and when I've installed all my Win 7 programs I'll just clean off the original XP disc, put the contents of E
rive D on to it and I'm
back where I started except on Win 7.